Showing papers on "Glycolysis published in 1986"

The lactate shuttle during exercise and recovery.

Abstract: Most (75%+) of the lactate formed during sustained, steady-rate exercise is removed by oxidation during exercise, and only a minor fraction (approximately 20%) is converted to glucose. Significant lactate extraction occurs during net lactate release from active skeletal muscle; the total lactate extraction approximates half the net chemical release. Of the lactate which appears in blood, most of this will be removed and combusted by oxidative (muscle) fibers in the active bed and the heart. The "shuttling" of oxidizable substrate in the form of lactate from areas of high glycogenolytic rate to areas of high cellular respiration through the interstitium and vasculature appears to represent an important means by which substrate is distributed, metabolic "waste" is removed, and the functions of various tissues are coordinated during exercise. During recovery from sustained exhausting exercise, most of the lactate accumulated during exercise will continue to be removed by direct oxidation. However, as the muscle respiratory rate declines in recovery, lactate becomes the preferred substrate for hepatic gluconeogenesis. Practically all of the newly formed liver glucose will be released into the circulation to serve as a precursor for cardiac and skeletal muscle glycogen repletion. Liver glycogen depots will not be restored, and muscle glycogen will not be completely restored until refeeding. This is because the diversion of lactate carbon to oxidation during exercise and recovery represents an irreversible loss of gluconeogenic precursor and because the processes of protein proteolysis and gluconeogenesis from amino acids are insufficient to achieve complete glycogen restitution after exhausting exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Human muscle metabolism during sprint running

Abstract: Biopsy samples were obtained from vastus lateralis of eight female subjects before and after a maximal 30-s sprint on a nonmotorized treadmill and were analyzed for glycogen, phosphagens, and glycolytic intermediates. Peak power output averaged 534.4 +/- 85.0 W and was decreased by 50 +/- 10% at the end of the sprint. Glycogen, phosphocreatine, and ATP were decreased by 25, 64, and 37%, respectively. The glycolytic intermediates above phosphofructokinase increased approximately 13-fold, whereas fructose 1,6-diphosphate and triose phosphates only increased 4- and 2-fold. Muscle pyruvate and lactate were increased 19 and 29 times. After 3 min recovery, blood pH was decreased by 0.24 units and plasma epinephrine and norepinephrine increased from 0.3 +/- 0.2 nmol/l and 2.7 +/- 0.8 nmol/l at rest to 1.3 +/- 0.8 nmol/l and 11.7 +/- 6.6 nmol/l. A significant correlation was found between the changes in plasma catecholamines and estimated ATP production from glycolysis (norepinephrine, glycolysis r = 0.78, P less than 0.05; epinephrine, glycolysis r = 0.75, P less than 0.05) and between postexercise capillary lactate and muscle lactate concentrations (r = 0.82, P less than 0.05). The study demonstrated that a significant reduction in ATP occurs during maximal dynamic exercise in humans. The marked metabolic changes caused by the treadmill sprint and its close simulation of free running makes it a valuable test for examining the factors that limit performance and the etiology of fatigue during brief maximal exercise.

Tissue intracellular acid-base status and the fate of lactate after exhaustive exercise in the rainbow trout.

Abstract: Exhaustive ‘burst-type’ exercise in the rainbow trout resulted in a severe acidosis in the white muscle, with pHi dropping from 7.21 to a low of 6.62, as measured by DMO distribution. An accumulation of lactate and pyruvate, depletions of glycogen, ATP and CP stores, and a fluid shift from the extracellular fluid to the intracellular fluid of white muscle were associated with the acidosis. The proton load was in excess of the lactate load by an amount equivalent to the drop in ATP, suggesting that there was an uncoupling of ATP hydrolysis and glycolysis. Initially, lactate was cleared more quickly than protons from the muscle, a difference that was reflected in the blood. It is suggested that during the early period of recovery (0–4 h), the bulk of the lactate was oxidized in situ, restoring pHi to a point compatible with glyconeogenesis. At that time, lactate and H+ were used as substrates for in situ glyconeogenesis, which was complete by 24 h. During this time, lactate and H+ disappearance could account for about 75% of the glycogen resynthesized. The liver and heart showed an accumulation of lactate, and it is postulated that this occurred as a result of uptake from the blood. Associated with the lactate load in these tissues was a metabolic alkalosis. Except for an apparent acidosis immediately after exercise, the acid-base status of the brain was not appreciably affected. Despite the extracellular acidosis, red cell pHi remained nearly constant.

A Novel Sucrose Synthase Pathway for Sucrose Degradation in Cultured Sycamore Cells

Abstract: Enzymes of sucrose degradation and glycolysis in cultured sycamore ( Acer pseudoplatanus L.) cells were assayed and characterized in crude extracts and after partial purification, in an attempt to identify pathways for sucrose catabolism. Desalted cell extracts contained similar activities (20-40 nanomoles per milligram protein per minute) of sucrose synthase, neutral invertase, glucokinase, fructokinase, phosphofructokinase, and UDPglucose pyrophosphorylase (assayed with 2 micromolar pyrophosphate (PPi). PPi-linked phosphofructokinase activity was virtually dependent upon fructose 2,6-bisphosphate, and the maximum activity exceeded that of ATP-linked phosphofructokinase. Hexokinase activity, with glucose as substrate, was highly specific for ATP, whereas fructokinase activity was relatively nonspecific. At 1 millimolar nucleoside triphosphate, fructokinase activity decreased in the order: UTP > ATP > CTP > GTP. We propose two pathways for sucrose degradation. One involves invertase action, followed by classical glycolysis of hexose sugars, and the other is a novel pathway initiated by sucrose synthase. The K m for sucrose of sucrose synthase was severalfold lower than that of neutral invertase (15 versus 65 millimolar), which may determine carbon partitioning between the two pathways. The sucrose synthase pathway proposed involves cycling of uridylates and PPi. UDPglucose pyrophosphorylase, which is shown to be an effective `PPi-scavenger,9 would consume PPi and form UTP. The UTP could be then utilized in the UTP-linked fructokinase reaction, thereby forming UDP for sucrose synthase. The source of PPi is postulated to arise from the back reaction of PPi-linked phosphofructokinase. Sycamore cells contained a substantial endogenous pool of PPi (about 3 nanomoles per gram fresh weight, roughly 1/10 the amount of ATP in these cells), and sufficient fructose 2,6-bisphosphate (0.09 nanomole per gram fresh weight) to activate the PPi-linked phosphofructokinase. Possible regulation and energetic differences between the sucrose synthase and invertase pathways are discussed.

A Novel Sucrose Synthase Pathway for Sucrose Degradation in

Abstract: Enzymes of sucrose degradation and glycolysis in cultured sycamore (Acer pseudoplatanus L.) cells were assayed and characterized in crude extracts and after partial purification, in an attempt to identify pathways for sucrose catabolism. Desalted cell extracts contained similar activities (20-40 nanomoles per milligram protein per minute) of sucrose synthase, neutral invertase, glucokinase, fructokinase, phosphofructokinase, and UDPglucose pyrophosphorylase (assayed with 2 micromolar pyrophosphate (PPi). PPi-linked phosphofructokinase activity was virtually dependent upon fructose 2,6-bisphosphate, and the maximum activity exceeded that of ATP-linked phosphofructokinase. Hexokinase activity, with glucose as substrate, was highly specific for ATP, whereas fructokinase activity was relatively nonspecific. At 1 millimolar nucleoside triphosphate, fructokinase activity decreased in the order: UTP > ATP > CIP > GTP. We propose two pathways for sucrose degradation. One involves invertase action, followed by classical glycolysis of hexose sugars, and the other is a novel pathway initiated by sucrose synthase. The Km for sucrose of sucrose synthase was severalfold lower than that of neutral invertase (15 versus 65 millimolar), which may determine carbon partitioning between the two pathways. The sucrose synthase pathway proposed involves cycling of uridylates and PPi. UDPglucose pyrophosphorylase, which is shown to be an effective 'PPi-scavenger,' would consume PPi and form UTP. The UTP could be then utilized in the UTP-linked fructokinase reaction, thereby forming UDP for sucrose synthase. The source of PPi is postulated to arise from the back reaction of PPi-linked phosphofructokinase. Sycamore cells contained a substantial endogenous pool of PPi (about 3 nanomoles per gram fresh weight, roughly l/lo the amount of ATP in these cells), and sufficient fructose 2,6-bisphosphate (0.09 nanomole per gram fresh weight) to activate the PPi-linked phosphofructokinase. Possible regulation and energetic differences between the sucrose synthase and invertase pathways are discussed.

Relationship of mitochondrial function and cellular adenosine triphosphate levels to hematoporphyrin derivative-induced photosensitization in R3230AC mammary tumors.

Abstract: The effects of hematoporphyrin derivative-induced photosensitization on the levels of adenosine triphosphate (ATP) in R3230AC mammary adenocarcinomas were studied. Enzymatically dissociated tumor cells were exposed to various doses of hematoporphyrin derivative (HPD) in vitro plus photoradiation. A drug and light dose-dependent decrease in cellular ATP levels was observed; ATP levels were reduced by 60% after treatment with 7.0 µg HPD per ml plus 0.72 J total energy density per cm2. Cell viability, assessed by exclusion of trypan blue, displayed an apparently coordinate behavior to ATP levels. The effects of hematoporphyrin derivative plus photoradiation were examined in the presence of oligomycin, an inhibitor of mitochondrial oxidative phosphorylation, or iodoacetate, an inhibitor of glycolysis, experiments designed to elucidate the site of action leading to reduced ATP levels. The results indicated that HPD-induced photosensitization had little additive effects to oligomycin-sensitive ATP production, whereas significant further reduction in ATP levels was obtained by HPD-induced photosensitization in the presence of iodoacetate. Taken together, along with earlier studies of selected mitochondrial enzymes, we conclude that HPD plus photoradiation inhibits mitochondrial function leading to reduction in cellular ATP levels and loss of viability.

Control of gluconeogenesis in rat liver cells. Flux control coefficients of the enzymes in the gluconeogenic pathway in the absence and presence of glucagon.

Abstract: We have used control analysis to quantify the distribution of control in the gluconeogenic pathway in liver cells from starved rats. Lactate and pyruvate were used as gluconeogenic substrates. The flux control coefficients of the various enzymes in the gluconeogenic pathway were calculated from the elasticity coefficients of the enzymes towards their substrates and products and the fluxes through the different branches in the pathway. The elasticity coefficients were either calculated from gamma/Keq. ratios (where gamma is the mass-action ratio and Keq. is the equilibrium constant) and enzyme-kinetic data or measured experimentally. It is concluded that the gluconeogenic enzyme pyruvate carboxylase and the glycolytic enzyme pyruvate kinase play a central role in control of gluconeogenesis. If pyruvate kinase is inactive, gluconeogenic flux from lactate is largely controlled by pyruvate carboxylase. The low elasticity coefficient of pyruvate carboxylase towards its product oxaloacetate minimizes control by steps in the gluconeogenic pathway located after pyruvate carboxylase. This situation occurs when maximal gluconeogenic flux is required, i.e. in the presence of glucagon. In the absence of the hormone, when pyruvate kinase is active, control of gluconeogenesis is distributed among many steps, including pyruvate carboxylase, pyruvate kinase, fructose-1,6-bisphosphatase and also steps outside the classic gluconeogenic pathway such as the adenine-nucleotide translocator.

ATP and the Regulation of Renal Cell Function

Abstract: pbetween these functions and ATP production in the kidney. Due to the cardinal role that the Na,K-ATPase plays in performing the work of the kidney, much of this review is directed toward aspects involving the metabolic support of the renal sodium pump. Other transport and metabolic processes performed by the kidney also require A TP, and several of these will also be discussed, as will several effects of extracellular ATP. Under steady-state conditions, the consumption of ATP by endergonic processes in the renal cell is matched by the production of A TP, resulting in the maintenance of a constant concentration of ATP within the cell. About 95% of the ATP in the kidney is supplied by oxidative metabolism (22, 63), and thus the renal mitochondria play an integral role in maintaining the energy-requiring processes of the kidney. From the renal rate of oxygen consumption (QOz), which varies between 3 and 6 f.Lmol Oz/min·g kidney for rat, dog, and rabbit (22, 89), and the assumption that 6 moles of ATP are produced by the mitochondria for every mole of O2 consumed, it can be calculated that the ATP turnover in the kidney is 18-36 f.Lmol ATP/min' g kidney. In this review several questions related to this synthesis will be considered, including: (a) what are the relative contributions to ATP synthesis from the heterogeneous segments of the

Muscle fatigue and lactic acid accumulation.

Abstract: Lactic acid is formed and accumulated in the muscle under conditions of high energy demand, rapid fluctuations of the energy requirement and insufficient supply of O2. During intense exercise sustained to fatigue muscle pH decreases to about 6.4-6.6. Force generation does not appear to be limited by the high H+ ion concentration per se but is more related to the PCr level. Phosphofructokinase may be inhibited by high H+ concentration but the inhibition is adequately overcome by increases in the activators AMP and ADP. A high concentration of H+ will decrease PCr by a direct effect on the creatine kinase equilibrium and indirectly by an increase in ADP. The effect of acidosis on glycolysis and on the PCr level will result in a decreased rate of ADP rephosphorylation, and it is suggested that ADP increases transiently above the steady-state level in the contracting muscle fibre. It is further suggested that the function of Na-K-ATPase is impaired by the increase of ADP resulting in an altered ionic balance over the muscle cell membrane. Muscle fatigue is thus considered to be due to an insufficient rate of ADP rephosphorylation resulting in a block in the activation process or in the excitation/contraction coupling.

Synaptosomal bioenergetics. The role of glycolysis, pyruvate oxidation and responses to hypoglycaemia.

Abstract: The bioenergetic interaction between glycolysis and oxidative phosphorylation in isolated nerve terminals (synaptosomes) from guinea-pig cerebral cortex is characterized. 1 Essentially all synaptosomes contain functioning mitochondria. 2 There is a tight coupling between glycolytic rate and respiration: uncoupler causes a tenfold increase in glycolysis and a sixfold increase in respiration. 3 Synaptosomes contain little endogenous glycolytic substrate and glycolysis is dependent on external glucose. 4 In glucose-free media, or following addition of iodoacetate, synaptosomes continue to respire and to maintain high ATP/ADP ratios. 5 In contrast to glucose, the endogenous substrate can neither maintain high respiration in the presence of uncoupler nor generate ATP in the presence of cyanide. 6 Pyruvate, but not succinate, is an excellent substrate for intact synaptosomes. 7 The in-situ mitochondrial membrane potential (ΔΨm) is highly dependent upon the availability of glycolytic or exogenous pyruvate; glucose deprivation causes a 20-mV depolarization, while added pyruvate causes a 6-mV hyperpolarization even in the presence of glucose. 8 Inhibition of pyruvate dehydrogenase by arsenite or pyruvate transport by α-cyano-4-hydroxycinnamate has little effect on ATP/ADP ratios; however respiratory capacity is severely restricted. 9 It is concluded that synaptosomes are valuable models for studying the control of mitochondrial substrate supply in situ.

Metabolic response of skeletal muscle to ischemia.

Abstract: To evaluate the temporal relationship and potential correlation between intramuscular phosphagen levels, lipid oxidation, and extent of muscle injury, a canine gracilis muscle model was used to study the consequences of a global ischemic episode for up to 7 h duration with reperfusion for 4 h. In this model the contralateral gracilis muscle was prepared identically to the test side but was not subjected to ischemia and thus served as a control. Blood flow, oxygen consumption, and lactate and glycerol release were measured before and after 2- and 7-h ischemic stress periods. The intramuscular metabolites, glycogen, lactate, phosphocreatine, and ATP, as well as free fatty acid conjugated dienes, were measured before, during, and after the ischemic insult. A 2-h ischemic insult resulted in minimal ultrastructural damage and complete regeneration of intramuscular phosphagens and glycogen on reperfusion with complete normalization of lipid oxidation products. In contrast, a 7-h ischemic insult resulted in profound injury at the ultrastructural level with an inability to restore intramuscular phosphagens and glycogen on reperfusion. This severe muscle injury correlated with a 2.5-fold increase in lipid oxidation products (free fatty acid conjugated dienes) and a decline in ATP levels below 5 mumol/g dry wt on reperfusion. Our results emphasize the prolonged glycolytic activity of skeletal muscle during global ischemia and document the increased production of oxygen free radical-mediated lipid oxidation products in irreversibly injured muscle.

Influence of hypoxia and an acidic environment on the metabolism and viability of cultured cells: potential implications for cell death in tumors

Abstract: Hypoxia and an acidic environment are known to occur in regions of solid tumors and might be involved in the causation of necrosis The viability and energy metabolism of cells in tissue culture were therefore investigated under hypoxic and/or acidic conditions Acute exposure of Chinese hamster ovary (CHO) cells or human bladder cancer MGH-U1 cells to hypoxia plus low pH (65 to 60) was cytotoxic in a time- and pH-dependent manner; surviving fraction was reduced to approximately 10(-4) following a 6-h exposure to hypoxia at pH 60 There was no effect on viability when aerobic CHO cells were exposed for 6 h at pH 60, or when either cell line was rendered hypoxic for 6 h at pH 70; MGH-U1 cells showed slight sensitivity to acidic pH in air Decrease in viability of CHO cells incubated under acid conditions was observed over the range of oxygen concentrations from 02 to 005%, similar to the range which causes change in cellular sensitivity to radiation Glucose consumption and lactate production by both cell lines were inhibited at low pH under both aerobic and hypoxic conditions Cellular adenosine triphosphate (ATP) levels and the energy charge [(ATP + 1/2 adenosine diphosphate)/(adenosine monophosphate + adenosine diphosphate + ATP)] of CHO cells were reduced by about 85 and 25%, respectively, after a 6-h exposure to hypoxia at pH 60 but were not influenced by hypoxia or acid pH alone Inhibition of glycolysis by incubation of CHO cells under hypoxic conditions in the absence of glucose (at pH 70) led to a larger fall in cellular ATP and energy charge, but cell survival fell to only approximately 10(-2) at 6 h These results demonstrate that hypoxia and an acid environment interact to cause marked toxicity A decrease in energy charge of the cells may contribute to loss of viability, but additional mechanisms appear to be involved

High glycogen levels enhance glycogen breakdown in isolated contracting skeletal muscle.

Abstract: The influence of supranormal muscle glycogen levels on glycogen breakdown in contracting muscle was investigated. Rats either rested or swam for 3 h and subsequently had their isolated hindquarters...

31P and 13C NMR studies of intermediates of aerobic and anaerobic glycolysis in Saccharomyces cerevisiae.

Abstract: The levels of intermediates of aerobic and anaerobic glycolysis were determined in perchloric acid extracts prepared from glycolyzing suspensions of Saccharomyces cerevisiae by 31P and 13C NMR spectroscopy. From 31P NMR measurements a small increase in the level of nucleoside triphosphates was found in derepressed cells upon oxygenation, while the ratio of nucleoside diphosphates to nucleoside triphosphates was a factor of 3 lower aerobically. Combined with the previous observation that the level of intracellular Pi is lower by a factor of 3 aerobically, this leads to the conclusion that the phosphate potential [NTP]/([NDP][Pi]) is lower by an order of magnitude during anaerobic glycolysis than during aerobic glycolysis. There was no correlation between the level of glucose 6-phosphate and the rate of glucose utilization. We used 13C NMR to determine the scrambling of the 13C label from C1 to C6 in fructose 1,6-bisphosphate (Fru-P2). There was more scrambling of the label during aerobic than during anaerobic glycolysis. Since the level of Fru-P2 did not change much upon oxygenation, this suggests that in aerobic glycolysis there is control of at least one enzyme in the lower part of the Embden-Meyerhof-Parnas pathway, below Fru-P2, which gives the 13C level more time to equilibrate between C1 and C6 of Fru-P2. Previous 13C NMR measurements of glucose utilization rates had shown a 2-fold reduction upon oxygenation, reflecting control in the early stages of the pathway.

Glycoconjugates as noninvasive probes of intrahepatic metabolism: pathways of glucose entry into compartmentalized hepatic UDP-glucose pools during glycogen accumulation

Abstract: Recent studies have questioned the efficiency with which administered glucose generates hepatic glycogen through the direct nonrecycling route compared with the indirect route from glucose recycled through glycolysis followed by gluconeogenesis. Using fasted and refed rats, we examined the relative access of infused [1-3H]- and [U-14C]glucose by way of these two pathways to liver glycogen and to hepatic glucuronic acid, the latter recovered from the urine as the glucuronide conjugated with administered acetaminophen. In fasted animals and during early refeeding, extensive dilution of administered [3H]- and [14C]glucose recovered in glycogen showed that 60-70% of the labeled glucose had undergone recycling by the indirect route. As refeeding progressed with substantial glycogen deposition, the contribution of the recycling pathway to glycogen and glucuronic acid diminished considerably. Thus, there is a shift in pathways of hepatic glucose utilization as liver glycogen accumulates. Consequently, the ratio of 3H/14C in glucuronic acid was closely correlated with the glycogen content of the liver at sacrifice, indicating that this ratio may prove useful as a noninvasive indicator of liver glycogen concentration. Since glycogen and glucuronic acid are derived by single reactions from UDP-glucose, they should show a common labeling pattern with 3H and 14C under various nutritional conditions. However, detailed analysis of their labeling patterns showed a striking divergence, implying that there must be compartmentation of the UDP-glucose pools leading to each of these end products, either because they are made in separate compartments within the same cell or because each is made in different hepatocyte populations. We favor the former explanation because galactose secreted in glycoproteins shows 3H and 14C labeling patterns similar to those of glucuronic acid conjugated with acetaminophen, and both of these conjugations occur in the endoplasmic reticulum of the liver, whereas most glycogen is present in the cytosol.

Studies on the regulation of yeast phosphofructo-1-kinase: its role in aerobic and anaerobic glycolysis.

Abstract: The kinetics of yeast phosphofructo-1-kinase has been studied in vitro. Effector concentrations (Fru-6-P, ATP, ADP, AMP, Pi, Fru-1,6-P2, and Fru-2,6-P2) and pH were adjusted so as to mimic intracellular concentrations in yeast. Under these conditions we were able to reproduce the measured in vivo rate of PFK. In addition, by reconstituting the intracellular conditions existing during aerobic and anaerobic glycolysis, we were able to reproduce in vitro the changes in the rate of PFK observed under these conditions. Without the addition of the newly discovered effector Fru-2,6-P2, in vitro rates of PFK are much lower than its in vivo rate. Changes in Fru-2,6-P2, Fru-1,6-P2, ATP, AMP, Pi, and pH in going from aerobic to anaerobic conditions all contributed somewhat to the change in the rate of PFK observed during the Pasteur effect, with no contribution coming from ADP. These studies show that the control of PFK under the condition of the Pasteur effect cannot be ascribed to changes in any one particular effector but rather to contributions from a variety of effectors. Also, the net change in the rate of PFK in the switch from anaerobic to aerobic glycolysis is small compared with the change in its dependence upon its substrate Fru-6-P, indicating a compensation mechanism.

Phosphofructokinase control in muscle: nature and reversal of pH-dependent ATP inhibition

Abstract: The kinetic and regulatory properties of rabbit muscle phosphofructokinase (PFK:EC 2.7.1.11) have been reexamined in an attempt to clarify how the enzyme could achieve significant catalytic rates over the physiological pH range (down to 6.4). At 5.0 mM ATP, the apparent Km for fructose 6-phosphate (fructose 6-P) increases by at least 50-fold as the pH is decreased from 7.67 to 6.8 in 50 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-KOH buffer at 25 degrees C (7.50 to 6.63 at 37 degrees C). This effect can be nearly completely abolished in the presence of 10 microM fructose 2,6-bisphosphate (fructose 2,6-P2), with the greatest percentage change seen at low pH. In this case, the rabbit enzyme behaves as if the ATP concentration was low (1.0 mM) at any given pH. Conversely, at high ATP levels and a low pH of 6.8 at 25 degrees C, PFK behaves in the presence of fructose 2,6-P2 as if the pH has been increased to approximately 7.15 or a 0.35 pH unit shift at any given fructose 6-P concentration. At physiological concentration of fructose 6-P (0.1 mM), the positive effectors glucose 1,6-bisphosphate (glucose 1,6-P2) and either AMP, inorganic phosphate, or NH4+ were found to be, respectively, 60 and 40% as effective as fructose 2,6-P2 in reversing this pH-dependent ATP inhibition over the physiological pH range. In combination, however, glucose 1,6-P2 plus AMP were as effective as fructose 2,6-P2.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional metabolism of experimental brain tumors

Abstract: Experimental brain tumors were produced in rats by stereotactical implantation of various neoplastic cell lines (RG 2, RG1 2.2, G 13/11, F 98, RN 6, B 104, and E 367). Using autoradiographic, bioluminescence, and fluoroscopic methods, the following regional hemodynamic and metabolic parameters were measured on intact brain sections: blood flow, glucose utilization, pH, and the tissue content of ATP, glucose, and lactate. Tumors exhibited a considerable diversity of regional blood flow and metabolic activity which did not correlate with the implanted cell line, location, or growth pattern. In solid regions of tumors the most consistent finding was a higher glucose utilization rate, a higher lactate, and a higher pH than in the surrounding brain tissue. Tumor ATP was slightly higher and glucose slightly lower than in the brain. In large spherical tumors a declining gradient of blood flow, glucose, and ATP from the periphery to the central parts was frequently observed, the decline being more pronounced for glucose than for ATP. In regions with high ATP tissue pH was usually higher than in the brain, but it decreased in areas in which ATP was depleted. The results obtained indicate that tumors are able to control tissue pH despite increased glycolysis and lactate production, as long as the energy state is not impaired. The mechanisms of pH regulation, therefore, have to be considered for establishing therapeutic procedures which intend to lower tumor pH for induction of tissue necrosis.

Arrestment of carbohydrate metabolism during anaerobic dormancy and aerobic acidosis inArtemia embryos: determination of pH-sensitive control points

Abstract: Changes in concentrations of trehalose, glycogen, glycerol, some glycolytic intermediates and adenylate nucleotides that occur during aerobic development have been compared to those seen during anaerobic dormancy and aerobic acidosis in gastrula-stage embryos ofArtemia. The latter two incubation conditions are known to foster large drops in intracellular pH (Busa et al. 1982; Busa and Crowe 1983). During aerobic development, trehalose levels decline while glycogen and glycerol are synthesized (Fig. 1). These transitions are blocked during both anaerobic dormancy and aerobic acidosis, but are resumed by return of embryos to aerobic incubation (Fig. 1). Thus, it is concluded that carbohydrate catabolism in hydrated embryos is directly modulated by intracellular pH. Changes in metabolite levels (Figs. 2–4) reveal that this process is controlled primarily at the trehalase and hexokinase reactions with a less-pronounced negative crossover point noted at the phosphofructokinase step. Each of these reactions is shown to be nonequilibrium by comparing the mass action ratio to the equilibrium constant (Table 1). When embryos are placed under anaerobic conditions, ATP levels drop dramatically while AMP increases in concentration (Fig. 5). These changes are reflected in a drop in adenylate energy charge from a control value of 0.73 to 0.42 (Fig. 6). Aerobic acidosis only leads to a slight decrease in energy charge, emphasizing that shifts in adenylate pools

Insulin-induced cytoplasmic alkalinization and glucose transport in muscle cells

Abstract: Insulin stimulates glucose uptake into muscle within minutes, preceding stimulation of glycolysis. Signals involved in stimulation of glycolysis include cytoplasmic alkalinization and specific intr...

Analysis of the energy metabolism after incubation of Saccharomyces cerevisiae with sulfite or nitrite.

Abstract: After addition of 5 mM sulfite or nitrite to glucose-metabolizing cells of Saccharomyces cerevisiae a rapid decrease of the ATP content and an inversely proportional increase in the level of inorganic phosphate was observed. The concentration of ADP shows only small and transient changes. Cells of the yeast mutant pet 936, lacking mitochondrial F1ATPase, after addition of 5 mM sulfite or nitrite exhibit changes in ATP, ADP and inorganic phosphate very similar to those observed in wild type cells. They key enzyme of glucose degradation, glyceraldehyde-3-phosphate dehydrogenase was previously shown to be the most sulfiteor nitrite-sensitive enzyme of the glycolytic pathway. This enzyme shows the same sensitivity to sulfite or nitrite in cells of the mutant pet 936 as in wild type cells. It is concluded that the effects of sulfite or nitrite on ATP, ADP and inorganic phosphate are the result of inhibition of glyceraldehyde-3-phosphate dehydrogenase and not of inhibition of phosphorylation processes in the mitochondria. Levels of GTP, UTP and CTP show parallel changes to ATP. This is explained by the presence of very active nucleoside monophosphate kinases which cause a rapid exchange between the nucleoside phosphates. The effects of the sudden inhibition of glucose degradation by sulfite or nitrite on levels of ATP, ADP and inorganic phosphate are discussed in terms of the theory of Lynen (1942) on compensating phosphorylation and dephosphorylation in steady state glucose metabolizing yeast.

Biochemical and physiological bases for lactate production.

Abstract: I have proposed an explanation of lactic acid production and output by red and white skeletal muscle during repetitive contractions. The proposal does not require O2 lack to slow oxidative phosphorylation. In this proposal lactic acid production is due to the fact that activation of glycolysis is more rapid than activation of oxidative phosphorylation. This results in a transient elevation of NADH in the cytoplasm and net lactic acid production. Once oxidative phosphorylation is fully activated and the activation of glycolysis wanes, balance is again achieved. Lactic acid production decreases and may become net utilization.