Showing papers on "Glycolysis published in 1983"

Carbohydrate metabolism in lactic acid bacteria.

Abstract: The term “lactic acid bacteria” is discussed. An overview of the following topics is given: main pathways of homo- and heterofermentation of hexoses, i.e. glycolysis, bifidus pathway, 6-phosphogluconate pathway; uptake and dissimilation of lactose (tagatose pathway); fermentation of pentoses and pentitols; alternative fates of pyruvate, i.e. splitting to formate and acetate, CO2 and acetate or formation of acetoin and diacetyl; lactate oxidation; biochemical basis for the formation of different stereoisomers of lactate.

Protein phosphatases: properties and role in cellular regulation

Abstract: Protein phosphorylation is a principal regulatory mechanism in the control of almost all cellular processes. The nature of the protein phosphatases that participate in these reactions has been a subject of controversy. Four enzymes, termed protein phosphatases 1, 2A, 2B, and 2C, account for virtually all of the phosphatase activity toward phosphoproteins involved in controlling glycogen metabolism, glycolysis, gluconeogenesis, fatty acid synthesis, cholesterol synthesis, and protein synthesis. The properties, physiological roles, and mechanisms for regulating the four protein phosphatases are reviewed.

Bioenergetics of intact human muscle. A 31P nuclear magnetic resonance study.

Abstract: The metabolic state of human muscle in various functional states has been investigated by the non-invasive technique of 31P nuclear magnetic resonance. The concentrations of phosphocreatine, ATP and inorganic phosphate as well as intracellular pH in the flexor digitorum superficialis have been measured during rest, dynamic exercise and recovery from exercise. The observed relationship between phosphocreatine utilization and decrease in intracellular pH during aerobic exercise indicates that lactate production only becomes significant after more than 60% of the phosphocreatine is used up. Surprisingly intracellular pH may reach as low a value as 5.9 to 6.1, indicating that phosphofructokinase is still partially active at pH 6.0. There is no metabolic recovery if the muscle is made ischaemic following exercise, implying that glycolysis is switched off as soon as exercise is stopped. Lactic acidosis is not the cause of this and presumably Ca2+ is needed to maintain the activation of phosphorylase kinase. The time-course of phosphocreatine recovery after exercise reflects the rate of oxidative metabolism, while pH recovery probably represents H+ ion export from the muscle cell. The dynamics of metabolic changes can now be observed with a time resolution of 10 to 60 seconds and thus disturbances in energy metabolism can be readily detected in several pathological states.

Gluconeogenesis and Related Aspects of Glycolysis

Abstract: PERSPECTIVES AND SUMMARy 618 GENERAL PROPERTIES OF GLUCONEOGENESIS AND GLYCOLYSIS IN THE LIVER 619 Gluconeogenesis 619 Glycolysis 619 Control Steps 620 ENZYME PROPERTIES 620 Pyruvate Carboxylase and Other Mitochondrial Involvement 620 Phosphoenolpyruvate Carboxykinase 623 Pyruvate Kinase 625 Fructose 1,6-Bisphosphatase 626 Fructose 2,6-Bisphosphatase 629 6-Phosphofructokinases 629 Glucose 6-Phosphatase 633 Glucokinase 634 THE CONTROL OF METABOLIC FLUX BY HORMONES AND OTHER EFFECTORS ...... 634 Cyclic AMP, Glucagon, and f3-Adrenergic Agents 634 Fructose 2,6-Bisphosphate 639 ex-Adrenergic Agents, Vasopressin, and Angiotensin 641 Glucocorticoids 643 Glucose 643 THE FUTILE CYCLES 644 Glucose/Glucose 6-Phosphate Cycle 644 Fructose 6-Phosphate/Fructose 1,6-Bisphosphate Cycle 646 Pyruvate/Phosphoenolpyruvate Cycle 647

Studies on the mechanism of the antifungal action of benzoate.

Abstract: A method is described for the determination of the pH of intracellular water based on the distribution of [14C]benzoate (0.01 mM) between intra- and extra-cellular water. Benzoate at higher concentrations (2-10mM) enters the yeast cell in the undissociated form, and its neutralization within the cell can cause a shift of the pH of the intracellular water by more than 1 pH unit. Benzoate causes an accumulation of the two hexose monophosphates of yeast glucose fermentation and a decrease in intermediates beyond phosphofructokinase, suggesting inhibition at this stage. Benzoate also causes a concomitant fall in [ATP]. Phosphofructokinase is inhibited to a greater extent than hexokinase at acid pH. There is a relationship between intracellular pH, phosphofructokinase inhibition and CO2 production, suggesting that the antifungal action of benzoate is caused by an accumulation of benzoate at low external pH, which lowers the intracellular pH into the range where phosphofructokinase is sensitive. The subsequent inhibition of glycolysis causes a fall in [ATP] and thus restricts growth.

Glycolytic promoters for regulated protein expression: protease inhibitor

Abstract: Promoters associated with expression of specific enzymes in the glycolytic pathway are used for expression of alien DNA, particularly yeast promoters known to provide high enzyme levels of enzymes in the glycolytic pathway are employed for expressing a mammalian protein, such as alpha-1-antitrypsin. The promoters include promoters involved in expression of pyruvate kinase, triose phosphate isomerase, phosphoglucose isomerase, phosphoglycerate mutase, hexokinase 1, hexokinase 2, glucokinase, phosphofructose kinase, and aldolase, as well as the glycolytic regulation gene. Particularly, the glycolytic regulation gene can be used in conjunction with promoters in the glycolytic pathway for regulated production of desired proteins.

Functional compartmentalization of oxidative and glycolytic metabolism in vascular smooth muscle.

Abstract: The metabolism of vascular smooth muscle is characterized by an unusual component of aerobic glycolysis. Lactate production, even under fully oxygenated conditions, is of similar magnitude to the rate of oxygen consumption when compared on a molar basis. Although the underlying mechanisms are unknown, the ratio of glycolytic to oxidative metabolism has been suggested to be an index of vascular myopathy. Measurements of the rate of O2 consumption (JO2), lactate production (Jlac), and isometric force in porcine coronary arteries were made under conditions known to alter both active force (delta Po) and Na+-K+ transport. As previously reported, JO2 was strongly correlated with delta Po; Jlac, however, was correlated with conditions that alter Na+-K+ transport. Under conditions known to inhibit Na+-K+ transport (10(-5) M ouabain, absence of extracellular K+ or Na+), Jlac was inhibited even though delta Po and JO2 were increased. The coupling of Na+-K+ transport with aerobic glycolysis was not dependent on tonicity or the major anion species, nor was it an effect simply on tissue lactate permeability as indicated by studies of tissue lactate content. Metabolic measurements made at similar levels of delta Po indicate that Jlac is markedly inhibited by ouabain, whereas JO2 shows little effect. Thus the unusual aerobic glycolysis observed in vascular smooth muscle appears to be linked to Na+-K+ transport processes and not to some nonspecific metabolic deficiency. Experiments on both systemic and pulmonary arteries from rat, rabbit, dog, and pig indicate that these results are not limited solely to porcine coronary vessels.

Compartmentation of glycolytic and glycogenolytic metabolism in vascular smooth muscle

Abstract: Vascular smooth muscle is characterized by a high rate of aerobic lactate production, which may be altered independently of oxidative phosphorylation. This finding suggested a cytoplasmic compartmentation of metabolism. Exogenous glucose was found to be the sole precursor of aerobic glycolysis under unstimulated conditions. Although tissue depolarization with high K+ resulted in a substantial reduction of endogenous glycogen, exogenous glucose remained the sole precursor of aerobic lactate production. These data showed unequivocally that carbohydrate metabolism is compartmentalized in vascular smooth muscle.

Structure and metabolism of mammalian liver glycogen monitored by carbon-13 nuclear magnetic resonance.

Abstract: Natural-abundance 13C NMR signals from glycogen are observable in situ within the perfused livers of rats. The nuclear magnetic relaxation properties (T1, T2, eta + 1) of glycogen were measured for glycogen in situ and in vitro and were found to be identical. All of the carbon nuclei in glycogen contribute to the high-resolution NMR spectrum, in spite of glycogen's very large molecular weight. The metabolism of glycogen in situ in the perfused rat liver was followed by 13C NMR. Stimulation of the fed rat liver by physiological glucagon levels led to rapid glycogenolysis. Perfusion of the liver with [1-13C]glucose led to net glycolysis, with concomitant scrambling of the label from C1 to C6 due to triosephosphate isomerase activity.

Atlantic hagfish cardiac muscle: metabolic basis of tolerance to anoxia

Abstract: Oxygen tensions in the major venous inputs to the systemic and portal-vein hearts of normoxic Atlantic hagfish (12.3 +/- 1.7 and 11.0 +/- 1.6 mmHg, respectively) are low compared with typical vertebrate values. Anoxia and poisoning with cyanide and azide do not significantly affect in situ performance of the systemic heart. Idoacetate poisoning, however, results in a significant decrease in cardiac performance of the systemic heart to 12% of the initial value after 3 h. Activities of mitochondrial enzymes of hagfish ventricle suggest a small potential for aerobic metabolism compared with those in the aerobic ventricle of Atlantic cod. Activities of enzymes of carbohydrate metabolism indicate similar anaerobic capacity in hagfish and cod ventricle. The ratio of pyruvate kinase to cytochrome c oxidase, an index of anaerobic to aerobic capacity, is 5.6 times greater in hagfish than cod ventricle. Metabolite concentrations in freeze-clamped ventricles of normoxic and hypoxic hagfish indicate hypoxia-induced activation of glycogenolysis, enhanced substrate flow across 6-phosphofructokinase, and an apparent secondary constriction of glycolysis at the level of glyceraldehyde-phosphate dehydrogenase. Carbohydrate utilization via the glycolytic pathway appears essential for maintenance of cardiac performance in both normoxic and anoxic hagfish. Under conditions of severe hypoxia, ATP provision is probably met by anaerobic glycolysis.

Glycolysis and brain function: [K+]o stimulation of protein synthesis and K+ uptake require glycolysis.

Abstract: Glucose is essentially the sole energy substrate in the normally functioning brain. There are, however, situations in which other substrates can partially substitute for glucose and maintain an apparently normal brain function. However, in no case has it been possible to completely substitute other substrates for glucose and maintain normal brain function. Studies on insulin-induced hypoglycemia suggest that this glucose dependence does not result from its involvement in ATP generation. Two explantation that have been offered are that toxic catabolites arise if nonglucose substrates are oxidized or that glycolysis is necessary to maintain neurotransmitter metabolism. We consider a third basis for the glucose requirement: our past studies have shown that hippocampal slice protein synthesis is activated by small increases in extracellular [K+] ([K+]o), and that this results from activation of K+ uptake into brain cells. We find that this process specifically requires aerobic glycolysis. The basis for the requirement appears to be that [K+]o activation of the Na+-K+ pump is specifically dependent on glycolytically generated energy. Thus, it is possible that glucose is required to maintain normal K+ clearance from the extracellular space during neural activity. This could partially account for the dependence of brain function on glycolysis.

Fibre type specific transformations in the enzyme activity pattern of rat vastus lateralis muscle by prolonged endurance training.

Abstract: The alterations in activity patterns of representative enzymes in energy metabolism were investigated in the superficial (white) and deep (red) portions of the fast vastus lateralis muscle of the adult rat in response to prolonged endurance training. It was found that following 15 weeks of extreme training (final running duration: 210 min per day, 27 m/min at 15 degree grade), increases in the activities of marker enzymes of the citric acid cycle (citrate synthase), beta-oxidation (3-hydroxyacyl CoA dehydrogenase), and ketone body utilization (3-ketoacid CoA transferase) as well as of glutamate pyruvate transaminase occurred in both regions of the muscle, with the greatest increase being observed in the superficial portion (2.6-4.2-fold). Pronounced increases were also seen for hexokinase which showed highest activities after 7 weeks of training. Conversely, decreases were noted for various glycogenolytic, glycolytic and gluconeogenic enzymes (phosphorylase, glyceraldehydephosphate dehydrogenase, pyruvate kinase, lactate dehydrogenase and fructose-1,6-diphosphatase). Reduction in the activities of these enzymes was most pronounced in the deep portion of the muscle. These results demonstrate a fundamental rearrangement of the energy metabolism of the muscle in response to prolonged, high intensity training. In the case of the deep portion of the vastus lateralis muscle, which has been shown to be composed of a large percentage of fast oxidative-glycolytic fibres (FOG), the enzyme profile becomes similar to the slow oxidative (SO) fibre. In the superficial portion which contains predominantly fast glycolytic fibres (FG), the enzyme profile becomes similar to FOG fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Diversity of Metabolic Patterns in Human Brain Tumors: Enzymes of Energy Metabolism and Related Metabolites and Cofactors

Abstract: Biopsies from 15 human gliomas, five meningiomas, four Schwannomas, one medulloblastoma, and four normal brain areas were analyzed for 12 enzymes of energy metabolism and 12 related metabolites and cofactors. Samples, 0.01-0.25 microgram dry weight, were dissected from freeze-dried microtome sections to permit all the assays on a given specimen to be made, as far as possible, on nonnecrotic pure tumor tissue from the same region. Great diversity was found with regard to both enzyme activities and metabolite levels among individual tumors, but the following generalities can be made. Activities of hexokinase, phosphorylase, phosphofructokinase, glycerophosphate dehydrogenase, citrate synthase, and malate dehydrogenase levels were usually lower than in brain; glycogen synthase and glucose-6-phosphate dehydrogenase were usually higher; and the averages for pyruvate kinase, lactate dehydrogenase, 6-phosphogluconate dehydrogenase, and beta-hydroxyacyl coenzyme A dehydrogenase were not greatly different from brain. Levels of eight of the 12 enzymes were distinctly lower among the Schwannomas than in the other two groups. Average levels of glucose-6-phosphate, lactate, pyruvate, and uridine diphosphoglucose were more than twice those of brain; 6-phosphogluconate and citrate were about 70% higher than in brain; glucose, glycogen, glycerol-1-phosphate, and malate averages ranged from 104% to 127% of brain; and fructose-1,6-bisphosphate and glucose-1,6-bisphosphate levels were on the average 50% and 70% those of brain, respectively.

Partial purification and regulatory properties of phosphofructokinase from Aspergillus niger.

Abstract: Phosphofructokinase (EC 2.7.1.11) from a citric acid-producing strain of Aspergillus niger was partially purified by the application of affinity chromatography on Blue Dextran--Sepharose and the use of fructose 6-phosphate and glycerol as stabilizers in the working buffer. The resulting preparation was still impure, but free of enzyme activities interfering with kinetic investigations. Kinetic studies showed that the enzyme exhibits high co-operativity with fructose 6-phosphate, but shows Michaelis--Menten kinetics with ATP, which inhibits at concentrations higher than those for maximal activity. Citrate and phosphoenolpyruvate inhibit the enzyme; citrate increases the substrate (fructose 6-phosphate) concentration for half-maximal velocity, [S]0.5, and the Hill coefficient, h. The inhibition by citrate is counteracted by NH4+, AMP and phosphate. Among univalent cations tested only NH4+ activates by decreasing the [S]0.5 for fructose 6-phosphate and h, but has no effect on Vmax. AMP and ADP activate at low and inhibit at high concentrations of fructose 6-phosphate, thereby decreasing the [S]0.5 for fructose 6-phosphate. Phosphate has no effect in the absence of citrate. The results indicate that phosphofructokinase from A. niger is a distinct species of this enzyme, with some properties similar to those of the yeast enzyme and in some other properties resembling the mammalian enzyme. The results of determinations of activity at substrate and effector concentrations resembling the conditions that occur in vivo support the hypothesis that the apparent insensitivity of the enzyme to citrate during the accumulation of citric acid in the fungus is due to counteraction of citrate inhibition by NH4+.

Intermediary metabolism in Legionella pneumophila: utilization of amino acids and other compounds as energy sources.

Abstract: The utilization of amino acids and other compounds as carbon and energy sources by Legionella pneumophila was examined. Based on the stimulation of oxygen consumption in washed-cell suspensions, glutamate, serine, threonine, and tyrosine were the only amino acids which were utilized as energy sources. Other stimulators of oxygen uptake were lactate, pyruvate, acetate, fumarate, and succinate. Citrate was a good stimulator only when the bacteria were grown in the presence of the substrate. Radiolabeling studies showed that [14C]glutamate was rapidly metabolized, with the label distributed evenly in all cell fractions. [14C]pyruvate and [14C]acetate were incorporated into the lipid-containing cell fraction, whereas glucose and glycerol were found in both the lipid- and polysaccharide-containing cell fractions. Radiorespirometry of differentially labeled [14C]glucose indicated that this compound was metabolized primarily by the pentose phosphate and Entner-Doudoroff pathways rather than by the glycolytic pathway.

Tricarboxylic acid cycle metabolites during ischemia in isolated perfused rat heart.

Abstract: Isolated rat hearts were, after a retrograde perfusion by the Langendorff procedure, rendered ischemic by lowering the aortic pressure to zero. The rate of proteolysis and temporal patterns of the changes in the concentrations of the metabolites of the tricarboxylic acid cycle, related amino acids, ammonia, and breakdown products of the adenine nucleotides were determined. The most significant change in the amino acid metabolism was a decrease of the proteolysis to one-tenth and a large accumulation of alanine, which was almost stoichiometric to the degradation of aspartate plus asparagine. The accumulation of malate and succinate was small compared with the metabolic net fluxes of aspartate and alanine. The metabolic balance sheet suggests that aspartate was converted to alanine. A prerequisite for this would be a feed in of carbon of aspartate to the tricarboxylic acid cycle as oxalacetate, reversal of the malate dehydrogenase, and production of pyruvate by the malic enzyme reaction. Alanine accumulating during ischemia is not glycolytic in origin but occurs through a concerted operation of anaplerotic reactions and tricarboxylic acid cycle metabolite disposal. The data also suggest that the potentially energy-yielding reduction of fumarate to succinate is not significant in the ischemic myocardium.

Potentiation of the actions of insulin by taurine.

Abstract: Taurine was found to mediate several changes in myocardial metabolism. In the absence of insulin, only oxygen consumption was significantly elevated by taurine; however, in the presence of 2.5 U/L insulin the amino acid caused the stimulation of glycolysis and glycogenesis, as well as oxygen utilization. These effects of taurine were shown to be dependent on insulin concentration, suggesting a link between the two substances. Measurements of key metabolic intermediates revealed that taurine stimulated glycolysis by enhancing flux through phosphofructokinase. Similarly, it was shown that glycogenesis was promoted because of the increase in glycogen synthase I and decrease in phosphorylase a activity. Several possible mechanisms for the observed changes are discussed.

Short-term modulation of glycogen metabolism, glycolysis and gluconeogenesis by physiological oxygen concentrations in hepatocyte cultures.

Abstract: The influence of different oxygen concentrations (0% to 20%, v/v) on the main pathways of carbohydrate metabolism was studied in rat hepatocyte cultures. Cells resembling the periportal or the perivenous cell type were obtained after 48 h culture under different hormonal conditions; they are referred to as 'periportal' or 'perivenous', respectively. Using radiochemical techniques the metabolic rates of the two cell types were measured between 48 h and 50 h under different oxygen tensions. Standard physiological substrates of 5 mM glucose, 2 mM lactate and endogenous glycogen were used. In cells incubated under 4% O2, mimicking hepatovenous oxygen levels, compared to cells assayed under 13% O2, mimicking arterial levels, glycogen degradation to free glucose and to lactate was faster while glycogen synthesis was slower; glycolysis, from glucose to lactate, was faster and gluconeogenesis, from lactate to glucose, was only slightly slower. Under anoxic conditions glycogen breakdown was maximal and glycogen synthesis minimal; gluconeogenesis was also minimal, but glycolysis was not maximal, it reached its peak rate at 4% O2. CO2-formation increased up to 6% and then stayed essentially constant at higher O2 tensions. Net glycogen metabolism: in 'perivenous' cells net glycogen synthesis was observed above, net glycogen degradation below 4% O2. In 'periportal' cells, which had a very low glycogen content, net glycogen metabolism was very small. Net glucose metabolism: in 'perivenous' cells net glucose formation was only seen under anoxic conditions. Net glucose utilization was observed at about the same rate under all physiological O2 tensions. In 'periportal' cells net glucose formation increased clearly up to 6% O2 and then remained almost constant. Net lactate metabolism: in 'perivenous' cells net lactate formation occurred below, and net lactate utilization above, 6% O2. In 'periportal' cells a pronounced net lactate utilization was observed under all physiological O2 tensions. Net flow between glucose-6-phosphate and pyruvate was observed in the glycolytic direction in 'perivenous' and in the gluconeogenic direction in 'periportal' cells except under anoxic conditions. When O2 tensions were lowered, the percentage of 'futile cycling' was decreased in the 'perivenous', glycolytic hepatocytes; conversely, it was increased in the 'periportal', gluconeogenic hepatocytes. It is concluded that physiological oxygen concentrations modulate hepatic carbohydrate metabolism and that they contribute further to the proposed metabolic differences between periportal and perivenous cells in vivo.

The effects of inhibition of oxidative phosphorylation and glycolysis on contractility and high-energy phosphate content in cultured chick heart cells.

Abstract: Cultured embryonic chick ventricular cells were exposed to various concentrations of cyanide ion to determine the relationships between graded inhibition of oxidative phosphorylation, contractile performance, and high energy phosphate contents. Exposure to cyanide produced a decline in contractile amplitude (CA) of cell motion of the spontaneously beating myocytes within 30–40 seconds. The threshold cyanide concentration for this effect was 10″5 M, and progressive increments in cyanide concentration produced further declines in contractile amplitude to 18% of control at a cyanide concentration of 1.5 × 10−4 M. Control values for adenosine triphosphate and phosphocreatine were 28.9 ± 0.08 and 17.9 ± 0.05 nmol/mg protein, respectively, and exposure of cultured cells to cyanide produced a decline in adenosine triphosphate concentration within 5–10 seconds. At low concentrations of cyanide, the decrement in high energy phosphate content paralleled the decline in contractile function after 10 minutes of cyanide exposure. However, as the concentration of cyanide was increased to above 10−4 M, high energy phosphate content did not decline below 50–60% of control values, despite further decrements in amplitude of contraction. Exposure of cultured cells to 10∼* M verapamil, which abolishes mechanical activity, resulted in preservation of high energy phosphate contents in cells exposed to cyanide at concentrations less than 10″4 M. However, there was no effect of verapamil on high energy phosphate contents in the presence of higher concentrations of cyanide. Exposure of these cells to inhibitors of glycolysis, 2-deoxyglucose (20 mM), or iodoacetate (10∼* M) resulted in a decline in contractile amplitude (55% of control after 10 minutes of exposure to 2-deoxylglucose) that was prevented by provision of the Krebs cycle substrates, acetate or pyruvate. However, glycolytic blockade with 2-deoxyglucose, in the presence of cyanide (10−4 M) and acetate, did produce further depression of contractile amplitude and high energy phosphate contents. These findings suggest that there is a quantitative relationship between the degree of depression of contractility and adenosine triphosphate and phosphocreatine levels only during mild-to-moderate degrees of inhibition of oxidative phosphorylation, and that negative inotropy during severe impairment of oxidative phosphorylation may preserve high energy phosphate. Energy derived from glycolysis, although not essential for maintenance of contractile function when oxidative phosphorylation is unimpeded and Krebs cycle substrate is provided, can contribute importantly to maintenance of high energy phosphate content and contractility during inhibition of oxidative phosphorylation.

Response to trauma of protein, amino acid, and carbohydrate metabolism in injured and uninjured rat skeletal muscles

Abstract: Soft tissue injury to one hindlimb produced trauma in rats without affecting their food intake or weight gain. Histologic examination showed damage to the soleus and gastrocnemius muscles but not to the extensor digitorum longus muscle. The protein content of the injured soleus muscle was lower than that of the contralateral soleus at one day after injury, and was reflected in vitro by a faster rate of protein degradation. The injured soleus also showed greater rates of protein synthesis, glucose uptake, glycolysis, oxidation of glucose, pyruvate, and leucine, and de novo synthesis of alanine. During three days after the injury, urinary nitrogen excretion increased progressively and was paralleled by a faster rate of protein degradation in uninjured muscles incubated with glucose, insulin, and amino acids. In these muscles, the inhibition of protein degradation by insulin diminished, while its stimulation of protein synthesis was unaffected. This insensitivity of proteolysis to insulin in trauma can explain the increased rate of this process. The oxidation of glucose and pyruvate were lower in the diaphragms of traumatized than of normal rats incubated with leucine, while glycolysis and uptake of 2-deoxyglucose did not differ. The degradation of leucine and isoleucine was greater in the diaphragms of traumatized animals and was associated with a faster de novo synthesis of alanine. For the uninjured soleus muscles of the traumatized rats, the slower rates of oxidation of glucose, glycolysis, and uptake of 2-deoxyglucose in the presence of insulin showed an insensitivity of glucose metabolism to this hormone. In contrast, no differences were seen in these various metabolic processes between the extensor digitorum longus muscles of traumatized and normal rats. These data suggest that the response of skeletal muscles to trauma may depend on their physiologic and biochemical characteristics.

Sensitivity to insulin of glycolysis and glycogen synthesis of isolated soleus-muscle strips from sedentary, exercised and exercise-trained rats.

Abstract: The half-maximal stimulation of the rates of glycolysis and glycogen synthesis in soleus-muscle strips from sedentary animals occurred at a concentration of insulin of about 100 microunits/ml. In soleus-muscle strips from exercise-trained rats (5 weeks of treadmill training), half-maximal stimulation of the rate of glycolysis occurred at about 10 microunits of insulin/ml, whereas that for glycogen synthesis occurred between 10 and 100 microunits of insulin/ml. The sensitivity of glycolysis to insulin after exercise training is similar to that of adipose tissue from sedentary animals. This finding suggests that, in sedentary animals, the effects of normal changes in insulin concentration may affect muscle primarily indirectly via the anti-lipolytic effect on adipose tissue, whereas after training insulin may effect the rate of glycolysis in muscle directly. A single period of exercise did not change the sensitivity of glycolysis in soleus muscle to insulin, nor probably that of glycogen synthesis. It is suggested that the improvement in insulin sensitivity of glycolysis in muscle caused by exercise-training could account, in part, for the well-established improvement in glucose tolerance and insulin sensitivity observed in man and rats after exercise-training.

Metabolic compartmentation of pyruvate in the isolated perfused rat heart.

Abstract: 1. Prompted by the finding of markedly differing specific radioactivities of tissue alanine and lactate in isolated rat hearts perfused with [1-14C]pyruvate, a more detailed study on the cytosolic subcompartmentalization of pyruvate was undertaken. Isolated rat hearts were perfused by the once-through Langendorff technique under metabolic and isotopic steady-state conditions but with various routes of radioactive label influx, and the specific radioactivities of pyruvate, lactate and alanine were determined. An enzymic method was devised to determine the specific radioactivity of C-1 of pyruvate. 2. Label introduction as [1-14C]pyruvate resulted in a higher specific radioactivity of tissue alanine and mitochondrial pyruvate than of lactate, and a higher specific radioactivity of perfusate lactate than of tissue lactate. Label introduction as [1-14C]lactate resulted in a roughly similar isotope dilution into the tissue and perfusate pyruvate and the tissue alanine. Label introduction as [3,4-14C]glucose resulted in the same specific radioactivity of tissue lactate and alanine and a roughly similar specific radioactivity of mitochondrial pyruvate. 3. The results can be reconciled with a metabolic model containing two cytosolic functional pyruvate pools. One pool (I) communicates more closely with the glycolytic system, whereas the other (II) communicates with extracellular pyruvate and intracellular alanine. Pool II is in close connection with intramitochondrial pyruvate. The physical identity of the cytosolic subcompartments of pyruvate is discussed.

The cardiac cycle: regulation and energy oscillations

Abstract: Cyclical changes in energy-related metabolites were observed in glucose-perfused but not pyruvate-perfused isolated working rat hearts. A chronological study of various phases of the cardiac cycle indicated maximum changes in metabolites occurred at half time to peak pressure (dF/dtmax). The high-energy phosphates ATP and phosphocreatine, as well as the glycolytic metabolites, glucose 6-phosphate and pyruvate, reached minimum values immediately prior to peak systole and maximum values during late diastole. The products of high-energy phosphate hydrolysis, ADP, inorganic phosphate, and creatine, as well as the regulator, adenosine 3',5'-cyclic monophosphate, showed the phase alternate. It was necessary to study cyclical changes in a maximally stressed glucose-perfused heart because the cyclical changes were small and appeared to be the result of rate-limiting steps in glycolysis and the slow transport of NADH into the mitochondria. For stressing the heart, thereby increasing ATP utilization and augmenting cyclical changes, the afterload chamber was set at 110 mmHg, and the perfusate contained high concentrations of calcium (3.5 mM, free) and isoproterenol (5 X 10(-9) M). When correction was made for binding and compartmentation of metabolites, data indicated that the free energy of ATP hydrolysis was preserved during the contraction process by a continuous binding and recycling of ADP.

The protein phosphatases involved in cellular regulation. 3. Fatty acid synthesis, cholesterol synthesis and glycolysis/gluconeogenesis.

Abstract: fatty acid synthesis and cholesterol synthesis in rat liver has been investigated using L-pyruvate kinase, ATP-citrate lyase, acetyl-CoA carboxylase and hydroxymethylglutaryl-CoA reductase as substrates. The results show that protein phosphatases-1, 2A and 2C are the only significant protein phosphatases in rat liver acting on these four substrates. The relationship of these three enzymes to other protein phosphatases described in the literature is discussed. Glycolysis, gluconeogenesis and the synthesis of lipids (fatty acid and cholesterol) are under hormonal control; several key regulatory enzymes in these metabolic pathways are known to be controlled by phosphorylation-dephosphor- ylation reactions. The conversion of phosphoenolpyruvate to pyruvic acid by L-pyruvate kinase is an important control point in both glycolysis and gluconeogenesis in mammalian liver. L-pyruvate kinase is phosphorylated on a single serine residue by cyclic-AMP-dependent protein kinase, increasing its

Anaerobic energy metabolism of the European eel, Anguilla anguilla L.

Abstract: Eels, acclimated the 15°C and aerated water (PO2 130 mm Hg) were exposed to hypoxia (PO2 lowered from 130 to 8 mm Hg in 4 h) and to complete anoxia until loss of equilibrium. Experiments were carried out at night. The mean survival time (LT50) during anoxic conditions proved to be 5.7 h. ATP, ADP, AMP, IMP, CrP, glycogen, lactate, pyruvate, α-ketoglutarate, malate, succinate, alanine, aspartate, glutamate and ammonia levels were determined in skeletal muscle and liver of control, hypoxic and anoxic fish. Some of the mentioned parameters were also measured in heart muscle and blood. Hypoxia causes declines of aspartate (muscle), CrP (muscle) and glycogen (liver, heart), and increases of alanine (blood, liver) and lactate (blood, liver, heart). During anoxia, muscle CrP stores are almost completely exhausted and adenylates are partially broken down to IMP. A decrease of glycogen and an accumulation of lactate were observed in all tissues examined. The energy charge of muscle and heart did not drop below 0.79, but in liver tissue it decreased from 0.65 to 0.17. Liver cytoplasm became significantly reduced during anoxia, but such a change of redox state did not occur in muscle. Eels seem to lack the capacity for anaerobic fermentation of glycogen to ethanol, as observed in goldfish. Lactate glycolysis and creatine phosphate breakdown appear to be the main energy producing pathways during anaerobiosis.

Alternatives to lactic acid: Possible advantages

Abstract: Many groups of invertebrates use metabolic strategies that do not lead to the accumulation of lactate during periods of hypoxia or anoxia. These animals may accumulate some combination of the following: alanine, octopine, alanopine, strombine, acetate, propionate, 2-methylbutyrate, 2-meth-ylvalerate, and succinate. An organism may derive a benefit from production of an alternative end product when the yield of ATP per mole of glucose 6-phosphate is greater than that found in lactate production. Formations of succinate, propionate, 2-methylbutyrate, and 2-methylvalerate have been shown to yield more ATP in a few species. This analysis can be extended to the formation of alanine, as this is accompanied by the conversion of aspartate to succinate. Formations of octopine, alanopine, or strombine apparently do not increase the yield of ATP per mole of glucose 6-phosphate, because the enzymes forming these compounds are functionally analogous to lactate dehydrogenase. A potential advantage of producing these compounds might be maintenance of a constant intracellular osmotic pressure during periods of anoxia. The significance of this is uncertain, because if lactate were to accumulate, the expected change in osmotic pressure appears to be trivial. Another possible advantage of accumulating octopine, alanopine, or strombine, would be the ability to maintain a lower NADH/NAD+ ratio as compared with the accumulation of lactate. This might assist the organism in maintaining a high rate of glycolysis by reducing the inhibition of glyceraldehyde 3-phosphate dehydrogenase by NADH. Other possibilities are smaller perturbations of the acid–base balance of the cell, or producing a compound that has less effect on the catalytic and regulatory properties of enzymes in the cell.