Showing papers on "Glycolysis published in 1979"
TL;DR: High-resolution phosphorus-31 nuclear magnetic resonance (31P NMR) spectra of wild-type and mutant strains of Saccharomyces cerevisiae were observed and each mutant strain was found to accumulate characteristic sugar phosphates when glucose was added to the cell suspension.
Abstract: High-resolution phosphorus-31 nuclear magnetic resonance (31P NMR) spectra of wild-type and mutant strains of Saccharomyces cerevisiae were observed at a frequency of 145.7 MHz. Levels of various phosphorus metabolites were investigated upon addition of glucose under both aerobic and anaerobic conditions. Three mutant strains were isolated and their biochemical defects characterized: pfk lacked phosphofructokinase activity; pgi lacked phosphoglucose isomerase activity; and cif had no glucose catabolite repression of the fructose bisphosphatase activity. Each mutant strain was found to accumulate characteristic sugar phosphates when glucose was added to the cell suspension. In the case of the phosphofructokinase deficient mutant, the appearance of a pentose shunt metabolite was observed. 31P NMR peak assignments were made by a pH titration of the acid extract of the cells. Separate signals for terminal, penultimate, and central phosphorus atoms in intracellular polyphosphates allowed the estimation of their average molecular weight. Signals for glycero(3)phosphochline, glycero(3)phosphoserine, and glycero(3) phosphoethanolamine as well as three types of nucleotide diphosphate sugars could be observed. The intracellular pH in resting and anaerobic cells was in the range 6.5--6.8 and the level of adenosine 5'-triphosphate (ATP) low. Upon introduction of oxygen, the ATP level increased considerably and the intracellular pH reached a value of pH 7.2--7.3, irrespective of the external medium pH, indicating active proton transport in these cells. A new peak representing the inorganic phosphate of one of the cellular organelles, whose pH differed from the cytoplasmic pH, could be detected under appropriate conditions.
248 citations
TL;DR: Under aerobic conditions, glucose is primarily catabolized by vascular smooth muscle to lactate, in spite of an adequate oxidative capacity, although this is often considered to be indicative of some nonspecific metabolic insufficiency.
Abstract: Under aerobic conditions, glucose is primarily catabolized by vascular smooth muscle to lactate, in spite of an adequate oxidative capacity. Although this is often considered to be indicative of some nonspecific metabolic insufficiency, there is evidence that aerobic glycolysis is specifically coupled to sodium and potassium transport processes, whereas oxidative metabolism is couple to contracticle energy requirements.
214 citations
TL;DR: No correlation of low or high levels of fructose-1,6-bisphosphate with the degree of catabolite repression and inactivation could be found, and this observation does not support the concept that hexose metabolites are directly involved in these regulatory mechanisms in yeast.
Abstract: Saccharomyces cerevisiae mutants unable to grow and ferment glucose have been isolated. Of 45 clones isolated, 25 had single enzyme defects of one of the following activities: phosphoglucose isomerase (pgi), phosphofructokinase (pfk), triosephosphate isomerase (tpi), phosphoglycerate kinase (pgk), phosphoglyceromutase (pgm), and pyruvate kinase (pyk). Phosphofructokinase activities in crude extracts of the pfk mutant were only 2% of the wild-type level. However, normal growth on glucose medium and normal fermentation of glucose suggested either that the mutant enzyme was considerably more active in vivo or, alternatively, that 2% residual activity was sufficient for normal glycolysis. All other mutants were moderately to strongly inhibited by glucose. Unusually high concentrations of glycolytic metabolites were observed before the reaction catalyzed by the enzyme which was absent in a given mutant strain when incubated on glucose. This confirmed at the cellular level the location of the defect as determined by enzyme assays. With adh (lacks all three alcohol dehydrogenase isozymes) and pgk mutants, accumulation of the typical levels of hexosephosphates was prevented when respiration was blocked with antimycin A. A typical feature of all glycolytic mutants described here was the rapid depletion of the intracellular adenosine 5′-triphosphate pool after transfer to glucose medium. No correlation of low or high levels of fructose-1,6-bisphosphate with the degree of catabolite repression and inactivation could be found. This observation does not support the concept that hexose metabolites are directly involved in these regulatory mechanisms in yeast.
175 citations
TL;DR: In the dark chloroplasts could metabolize all the products of starch breakdown and catalyse much of the respiration of pea shoots via the oxidative pentose phosphate pathway and/or glycolysis as far as 3-phosphoglycerate, and it is suggested that pea shoot chloroplast lack phosphoglyceromutase but contain some phosphopyruvate hydratase and pyruvating kinase.
147 citations
TL;DR: The physiological and possible therapeutic role of carnitine, a vitamin essential for normal fatty acid oxidation, and its physiological and biochemical functions are still being elucidated are analyzed.
145 citations
TL;DR: It is proposed that insulin regulates lipoprotein lipase in fat cells by three major actions: it elicits a rapid release of enzyme from the cell through mechanisms which are independent of energy metabolism and protein synthesis; it stimulates gene expression and synthesis of RNA independently of effects on hexose and amino acid transport; and it stimulates expression of the nuclear effects of the hormone at the translational level.
143 citations
TL;DR: Phosphofructokinase appears to be phosphorylated in vivo by a cyclic AMP-dependent protein kinase, which renders the enzyme significantly more sensitive to ATP inhibition and exhibits considerably lower activity than the unphosphorylated enzyme.
112 citations
TL;DR: The neural components of peripheral nerve are probably dependent on glucose as their major substrate for energy production and respiration under most physiologic conditions in which elevated plasma ketone body concentrations are absent; their composite glucose utilization is not subject to acute, direct regulation by insulin in concentrations that might reasonably be derived from plasma insulin of pancreatic origin.
Abstract: An "endoneurial" preparation from a rabbit tibial nerve fascicle was used to study the ability of peripheral nerve axons and Schwann cells to derive their composite energy requirements from glucose, D-beta-hydroxybutyrate, or albumin-bound palmitate, and the effects of insulin in vitro on their composite glucose utilization. Samples incubated with 5 mM glucose for 2 h maintained a stable O2 uptake and P-creatine and ATP concentrations, and they exhibited a slight increase in P-creatine/creatine ratio (the electron microscopic appearance of the preparation was previously shown to be unaltered under these conditions). The rate of glucose oxidation required to account for the O2 uptake accounted for 61% of the glucose uptake. In samples incubated without substrate for 2 h, a marked fall in tissue glucose was associated with a 50% decrease in O2 uptake and with decreases in P-creatine, ATP, and in the P-creatine/creating ratio. In medium lacking glucose but containing 5 mM DL-beta-hydroxybutyrate, a stable rate of D-beta-hydroxybutyrate uptake was observed, and acetoacetate production accounted for only a small fraction; significant decreases in O2 uptake or ATP were prevented, and, although P-creatinde and the P-creatine/creatine ratio fell, they remained significantly higher than after incubation without substrate. An efficient blood-nerve barrier to albumin is known to exist. Medium containing albumin-bound palmitate with molar ratios or palmitate/albumin of 1 or 2 (highest FFA concentration, 1.32 meq/L) failed to prevent decreases in P-creatine, ATP, and in the P-creatine/creatine ratio during incubations without glucose; the associated O2 uptakes suggested that the tissue is susceptible to respiratory uncoupling and depression son exposure to albumin-blund palmitate as compared with non-neural tissue. Insulin (100 or 1000 microU/ml) had no detectable effects on glucose utilization in the endoneurial preparation during 2-h incubations with 5 mM glucose or (U-14C) glucose. In contrast, in epineurial tissue from rabbit sciatic nerve, insulin (100 micronU/ml) increased (U-14C) glucose incorporation into CO2 and total lipid. The neural components of peripheral nerve are probably dependent on glucose as their major substrate for energy production and respiration under most physiologic conditions in which elevated plasma ketone body concentrations are absent; their composite glucose utilization is not subject to acute, direct regulation by insulin in concentrations that might reasonably be derived from plasma insulin of pancreatic origin.
95 citations
TL;DR: The idea that citrate lyase may play an important role in lipogenesis in hyperplastic human breast tissues is supported.
Abstract: Activities of some enzymes associated with carbohydrate and lipid metabolism were determined in 48 human breast carcinomas and compared with those found in 35 nonmalignant breast tumours and also in 13 normal breast tissues. In fibrocystic disease only the activity of citrate lyase was markedly higher (14-fold) than in normal tissue. The activities of the remaining enzymes did not differ significantly from those in normal tissue. Enzyme activities in breast carcinoma were 4--160 x those determined in normal tissue according to the following sequence : phosphofructokinase less than malate NADP dehydrogenase less than hexokinase less than lactate dehydrogenase less than isocitrate NADP dehydrogenase less than ATP citrate lyase. Activity of citrate lyase, very low in normal breast (0.0017 mumol/min/g of tissue) rose gradually to 0.039, 0.072 and 0.258 mumol/min/g of tissue in localized fibrocystic disease, fibroadenomas and carcinomas respectively. These data support the idea that citrate lyase may play an important role in lipogenesis in hyperplastic human breast tissues.
90 citations
TL;DR: An indication of the metabolic capacity of the plastids was determined by monitoring the ribulose-1,5-bisphosphate carboxylase activity in the endosperm.
Abstract: During castor oil seed development, changes occur in the activities of enzymes involved in fatty acid biosynthesis, glycolysis, and the pentose phosphate pathways. The activities of acetyl-CoA carboxylase, phosphofructokinase, pyruvate kinase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase per seed increase during the phase of rapid oil synthesis in the endosperm. As the seed matures and the rate of fatty acid synthesis decreases, there is a corresponding diminution in the activities of these enzymes. An indication of the metabolic capacity of the plastids was determined by monitoring the ribulose-1,5-bisphosphate carboxylase activity in the endosperm.
82 citations
TL;DR: The failure of McN-3716 to inhibit the oxidation by diaphragm of short-chain fatty acids, palmitoyl camitine, glucose, glycolytic intermediates, β-hydroxybutyrate, succinate, or citrate when added in vitro or after treatment of rats suggests that glycoleysis, the tricarboxylic acid cycle, and the intramitochondrial β-oxidation of fatty acids were not inhibited.
Abstract: The oral hypoglycemic agents methyl 2-tetradecylglycidate (McN-3716) and 2-tetradecylglycidic acid (McN-3802), synthesized in an effort to design a specific inhibitor of long-chain free fatty acid (FFA) oxidation, were tested for their effects on rat hemidiaphragm oxidation of various substrates to CO2. When added in vitro, both compounds were more potent (100-1000 times) in inhibiting long-chain FFA oxidation than either a-bromopalmitic or 4-pentenoic acid. When fasting normal or diabetic rats were pretreated with McN-3716, the ability of the diaphragms to oxidize palmitate-1-l4C to 14CO2 incubated in vitro was also diminished. Closely related nonhypoglycemic analogs of McN-3716 failed to inhibit oxidation. The failure of McN-3716 to inhibit the oxidation by diaphragm of short-chain fatty acids, palmitoyl camitine, glucose, glycolytic intermediates, β-hydroxybutyrate, succinate, or citrate when added in vitro or after treatment of rats suggests that glycolysis, the tricarboxylic acid cycle, and the intramitochondrial β-oxidation of fatty acids were not inhibited. While depressing FFA oxidation, McN-3716 increased the ability of hemidiaphragms from normal and diabetic rats to oxidize glucose-14C to 14CO2. This supports an intimate relationship between FFA oxidation and glucose utilization in hemidiaphragm. The locus of this stimulation appears to be the glycolytic pathway. The earliest onset for the impairment of diaphragm muscle FFA oxidation and the rise of plasma FFA after treatment of fasting rats with McN-3716 preceded the stimulation of hemidiaphragm glucose oxidation and the lowering of plasma glucose and tissue glycogen stores. These results suggest that the carbohydrate changes are secondary to the inhibition of FFA oxidation.
TL;DR: It is concluded that this inhibition can be accounted for by accumulation of H+, NADH and lactate in the ischemic tissue and the combined effect of these three inhibitors probably accounts for the inhibition that is observed.
TL;DR: The effects of phenazine methosulfate on the incorporation of glucose into glyceride glycerol, on the flux of glucose through the pyruvate dehydrogenase reaction and tricarboxylic acid cycle, all processes linked to the NAD + NADH couple, appeared to be minimal in the brain at the stages of development studied.
TL;DR: Viewed in the context of conditions that may be encountered in skeletal muscle in vivo, oscillatory behavior of glycolysis is shown to have additional advantages for maintaining a high [ATP]/[ADP] ratio.
TL;DR: It is concluded that there may be much larger changes in the free concentration of oxaloacetate than are indicated by theChanges in the total content of this metabolite or that other unknown factors must play an additional role in the regulation of citrate synthase activity.
Abstract: 1. The contents of some intermediates of glycolysis, the citric acid cycle and adenine nucleotides have been measured in the freeze-clamped locust flight muscle at rest and after 10s and 3min flight. The contents of glucose 6-phosphate, pyruvate, alanine and especially fructose bisphosphate and triose phosphates increased markedly upon flight. The content of acetyl-CoA is decreased after 3min flight whereas that of acetylcarnitine is decreased markedly after 10s flight, but returns towards the resting value after 3min flight. The content of citrate is markedly decreased after both 10s and 3min flight, whereas that of isocitrate is changed very little after 10s and is increased by 50% after 3min. The content of oxaloacetate is very low in insect flight muscle and hence it was measured by a sensitive radiochemical assay. The content of oxaloacetate increased about 2-fold after 3min flight. A similar change was observed in the content of malate. The content of ATP decreased about 15%, whereas those of ADP and AMP increased about 2-fold after 3min flight. 2. Calculations based on O(2) uptake of the intact insect indicate that the rate of the citric acid cycle must be increased >100-fold during flight. Consequently, if citrate synthase catalyses a non-equilibrium reaction, the activity of the enzyme must increase >100-fold during flight. However, changes in the concentrations of possible regulators of citrate synthase, oxaloacetate, acetyl-CoA and citrate (which is an allosteric inhibitor), are not sufficient to account for this change in activity. It is concluded that there may be much larger changes in the free concentration of oxaloacetate than are indicated by the changes in the total content of this metabolite or that other unknown factors must play an additional role in the regulation of citrate synthase activity. 3. The increased content of oxaloacetate could be produced via pyruvate carboxylase, which may be stimulated during the early stages of flight by the increased concentration of pyruvate. 4. The decreases in the concentrations of citrate and alpha-oxoglutarate indicate that isocitrate dehydrogenase and oxoglutarate dehydrogenase may be stimulated by factors other than their pathway substrates during the early stages of flight. 5. Calculated mitochondrial and cytosolic NAD(+)/NADH ratios are both increased upon flight. The change in the mitochondrial ratio indicates the importance of the intramitochondrial ATP/ADP concentration ratio in the regulation of the rate of electron transfer in this muscle.
TL;DR: It is suggested that the mechanism for the high rate of aerobic glycolysis in papilla tissue in the presence of an adequate O2 supply is due to the relatively small mass of mitochondria in papillary tissue in relation to the amount of work done by the tissue.
Abstract: It is widely accepted that in vivo the function of the papilla of the mammalian kidney is supported primarily by anaerobic metabolism. As a result, the major source of energy for support of function in the papilla is considered to be derived from glycolysis. This orientation originates from two concepts: 1) that in vivo the gaseous environment of the papilla has such a low PO2 that O2 availability limits O2 consumption, and 2) that papillary tissue has a high rate of glycolysis when compared with either cortical tissue or extrarenal tissues. It has also been tacitly assumed that papillary tissue has a "low" O2 uptake. Review of the measurements of PO2 of papillary tissue and of urine PO2 indicates that the PO2 of papillary tissue should not limit its aerobic mitochondrial oxidative metabolism. While the rate of aerobic glycolysis in papillary tissue is high, simultaneously papillary tissue has a rate of O2 uptake similar to that of liver and higher than that of muscle. The major (two-thirds) source of energy for papillary tissue in vitro is from O2 uptake. That papillary tissue is not exclusively dependent on glucose for its energy requirements is indicated by the greater stimulation of papillary tissue QO2 by succinate than by glucose. Thus, papillary tissue has both a high aerobic mitochondrial oxidative metabolism and a high aerobic glycolytic metabolism. It is suggested that the mechanism for the high rate of aerobic glycolysis in the presence of an adequate O2 supply is due to the relatively small mass of mitochondria in papillary tissue in relation to the amount of work done by the tissue. As a result of the limited rate of ATP production by the mitochondrial electron transport chain, the phosphorylation state ([ATP]/[ADP][Pi]) is reduced and the cytoplasmic redox state ([NAD+]/[NADH]) of the papillary collecting duct cells also becomes more reduced; changes in both ratios enhance the rate of glycolysis. This limited metabolic capacity of the collecting duct cells may permit an excess volume of solute and water to be excreted during volume expansion diuresis. The metabolic characteristics of the papilla, when compared to cortex, also provide a basis for the observed differences in substrate selectivity of cortex and medulla with respect to utilization of glucose and lactate. The experimental approaches that may provide information bearing on the suggested mechanisms for regulation of papillary metabolism in relation to tubular work functions are indicated.
TL;DR: It is concluded that insufficient glucose was moved through the circulation to account for the rate of glycogen formation observed in the recovering exhausted muscle.
Abstract: The conclusion from two in vivo experiments is that a significant proportion of the lactic acid, normally formed by glycolysis from glycogen and held in the muscle cells following exhausting exercise of the anaerobic swimming muscle of the teleost fish Pleuronectes platessa L, is converted by gluconeogenesis to form glycogen in the recovering muscle.
In the first experiment a technique for measurement of [3H]glucose turnover in the plaice was developed and applied to measure turnover in resting and exhausted fish. It is concluded that insufficient glucose was moved through the circulation to account for the rate of glycogen formation observed in the recovering exhausted muscle.
In the second experiment, an intramuscular injection of [14C]lactate to exhausted fish revealed a direct uptake of [14C]lactate by the recovering muscle cells, and the incorporation of substantial proportions of lactate into the restored glycogen. Simultaneous use of [3H]-mannitol allowed measurement of the isotope distribution between extra- and intracellular spaces.
TL;DR: The mechanisms whereby glucose reduces fatty acid-induced release of enzyme from the coronary-ligated isolated perfused working rat heart are investigated and provision of glycolytic ATP from increased glyCOlytic flux may be one important factor.
Abstract: The mechanisms whereby glucose reduces fatty acid-induced release of enzyme from the coronary-ligated isolated perfused working rat heart are investigated. Alterations in the tissue contents of ATP, phosphocreatine, or glycogen could be excluded as possible mechanisms for the beneficial effect of glucose in this system. Provision of glycolytic ATP from increased glycolytic flux may be one important factor.
TL;DR: Results show that the hypothesis of allosteric regulation of phosphofructokinase ( by PEP) and PEP carboxylase (by malate and glucose-6-P) cannot provide a complete explanation for the temporal organization of glycolysis and that changes in the phase relationships between the rhythms of enzyme capacity along the pathway are important components of the regulation of gly colysis in relation to CAM.
Abstract: Glycolysis shows different patterns of operation and different control steps, depending on whether the level of Crassulacean acid metabolism (CAM) is low or high in the leaves of Kalanchoe blossfeldiana v.Poelln., when subjected to appropriate photoperiodic treatments: at a low level of CAM operation all the enzymes of glycolysis and phosphoenol pyruvate (PEP) carboxylase present a 12 h rhythm of capacity, resulting from the superposition of two 24h rhythms out of phase; phosphofructokinase appears to be the main regulation step; attainment of high CAM level involves (1) an increase in the peak of capacity occurring during the night of all the glycolytic enzymes, thus achieving an over-all 24h rhythm, in strict allometric coherence with the increase in PEP carboxylase capacity, (2) the establishment of different phase relationships between the rhythms of enzyme capacity, and (3) the control of three enzymic steps (phosphofructokinase, the group 3-P-glyceraldehyde dehydrogenase — 3-P-glycerate kinase, and PEP carboxylase). Results show that the hypothesis of allosteric regulation of phosphofructokinase (by PEP) and PEP carboxylase (by malate and glucose-6-P) cannot provide a complete explanation for the temporal organization of glycolysis and that changes in the phase relationships between the rhythms of enzyme capacity along the pathway and a strict correlation between the level of PEP carboxylase capacity and the levels of capacity of the glycolytic enzymes are important components of the regulation of glycolysis in relation to CAM.
TL;DR: Fetal hyperinsulinemia with euglycemia increases the activity of enzymes that participate in lipogenesis, decreases some of those controlling gluconeogenesis, and has no effect on the enzymes of glycolysis.
Abstract: Hyperinsulinemia was produced in fetal rhesus monkeys for 21 days in the last third of gestation by subcutaneous pork insulin injected at 19 U a day. Plasma insulin concentrations in treated fetuses ( N = 4) were 3525 μU/ml compared with controls' ( N = 6) 51 μ/ml. There was no difference in paired pre- and post-treatment fetal plasma glucose concentration. Activity of the hepatic enzymes that promote glucose utilization (glucokinase and hexokinase) and glycolysis (phos-phofructokinase, pyruvate kinase, and pyruvate dehy-drogenase) was unaffected. Similarly, glycogen metabolism enzymes (active and inactive synthase and phosphorylase) were unaltered. Two gluconeogenic enzymes (PEPCK and glucose-6-phosphatase) were diminished in the treated group compared with controls. Fetal hyperinsulinemia enhanced lipogenic and NADPH-producing enzyme activities, as evidenced by a twofold increase in fatty acid synthase and in citrate cleavage enzyme activity. Malic enzyme was absent. Hyperinsulinemia with euglycemia (1) increases the activity of enzymes that participate in lipogenesis, (2) decreases some of those controlling gluconeogenesis, and (3) has no effect on the enzymes of glycolysis.
TL;DR: Experiments with [1-(14)C]arabinose indicated that pentose was fermented by a pentose phosphate cycle plus glycolysis, with some indication of a minor phosphoketolase-type pathway, and adenosine 5'-triphosphate molar growth yields could not be calculated with any certainty.
Abstract: Metabolism and growth yields of Bacteroides ruminicola grown on d-xylose, l-arabinose, and l-rhamnose were studied. Growth yields were 62, 68, and 35.5 g (dry weight) per mol of carbohydrate fermented after correction for storage polysaccharide. Experiments with [1-(14)C]arabinose indicated that pentose was fermented by a pentose phosphate cycle plus glycolysis, with some indication of a minor phosphoketolase-type pathway. The product ratios from pentose were similar to those previously described for hexose. Rhamnose was fermented mainly to 1,2-propanediol, succinate, and acetate, although the latter was quantitatively less than expected. Estimates of adenosine 5'-triphosphate (ATP) molar growth yields could not be calculated with any certainty, as ATP generation by electron transport-linked phosphorylation cannot yet be assessed. If ATP were generated by substrate-level phosphorylation reactions alone, ATP molar growth yields for xylose, arabinose, and rhamnose would be 30, 28, and 35 g/mol. If calculations are based on an assumption that two ATP are generated by electron transport-linked phosphorylation per succinate, ATP molar growth yields become 15, 14, and 22 g/mol; if the assumption is also made that the pathway of lactaldehyde reduction is coupled to production of one ATP per 1,2-propanediol by electron transport-linked phosphorylation, the ATP molar growth yield for rhamnose fermentation becomes 14 g/mol. No preference can be expressed between these alternatives at present.
TL;DR: Results implicate a second site of inhibition of fatty acid synthesis by Bt(2)cAMP that involves the utilization, but not the production, of cytoplasmic acetyl-CoA.-Clarke, S. D., P. A. Watkins, and M. Lane.
TL;DR: Quantitatively, anaerobic glycolysis accounts for a maximum of 28% of basal aerobic ATP generation, suggesting that prolonged diving is also accompanied by a reduction in brain energy requirements, and the adaptation subserving short-term (natural) diving is an increase in brain Glycolytic capacity.
Abstract: The adaptations in the freshwater turtle that permit survival despite prolonged loss of mitochondrial ATP generation were investigated by comparing the bioenergetics of turtle brain slices with rat brain slices. Aerobic turtle brain shows no significant difference in basal levels of total ATP generation compared to rat brain; levels in turtle brain and rat brain were 18.4 +/- 2.8 (SD) and 19.4 +/- 2.2 mumol (100 mg of tissue)-1 hr-1, respectively. However, in turtle brain, a significantly greater fraction of ATP is derived from glycolysis both under aerobic and anaerobic conditions [aerobic turtle (24%) and rat (13%), P less than 0.02; anaerobic, turtle (28%) and rat (18%), P less than 0.05]. The increased glycolytic capacity is related to high levels of rate-limiting glycolytic enzymes, such as pyruvate kinase (EC 2.7.1.40). Turtle brain operates close to glycolytic capacity even under aerobic conditions, and no Pasteur effect can be demonstrated. Quantitatively, anaerobic glycolysis accounts for a maximum of 28% of basal aerobic ATP generation, suggesting that prolonged diving is also accompanied by a reduction in brain energy requirements. The adaptation subserving short-term (natural) diving is an increase in brain glycolytic capacity. The adaptation subserving prolonged diving (days to weeks) may be a reduction in the energy requirements of brain (and other cells).
TL;DR: The futile cycle of fructose 1,6-bisphosphate synthesis and degradation during glycolysis is partially avoided, but the cells are poised for rapid adaptation upon change to gluconeogenic growth conditions.
TL;DR: The data indicate that insulin release can be stimulated by non‐metabolizable secretagogues, despite a fall in the concentration of both ATP and NAD(P)H, however, the insulinotropic action of glucose, whatever its concentration, may depend on an increased generation of both reducing equivalents and high‐energy phosphate intermediates.
Abstract: The combination of Ba2+ and theophylline provoked a dramatic release of insulin from rat pancreatic islets incubated in the absence of extracellular Ca2+. The secretory response was unaffected by poisons of glycolysis; inhibited by epinephrine, organic calcium‐antagonists, respiratory inhibitors, and uncoupling agents; and augmented by glucose, 2‐oxoisocaproate and 2‐oxoiso‐valerate. The latter augmentation occurred even when the nutrients were used at concentrations which did not stimulate insulin release from islets maintained in a normal ionic environment. The release of insulin evoked by the combination of Ba2+ and theophylline was associated with an increase in the rate of oxidation of endogenous nutrients, but a fall in the concentration of both ATP and reduced pyridine nucleotides. The facilitation of insulin release by glucose (3.3 and 16.7 mM) was associated with a dose‐related increase in both the concentration of NAD(P)H and net uptake of 133Ba. The magnitude of the augmenting action of glucose upon insulin release evoked by the combination of Ba2+ and theophylline correlated with the rate of glucose oxidation. These data indicate that insulin release can be stimulated by non‐metabolizable secretagogues, despite a fall in the concentration of both ATP and NAD(P)H. However, the insulinotropic action of glucose, whatever its concentration, may depend on an increased generation of both reducing equivalents and high‐energy phosphate intermediates. Copyright © 1979, Wiley Blackwell. All rights reserved
Journal Article•
TL;DR: A direct relationship between the differences was found for the activities of some enzymes belonging to carbohydrate metabolism, namely, hexokinase, pyruvate kinase, aldolases A and B, glucose-6-phosphate dehydrogenase, and phosphogluconate dehydrogensase and the differences found for glucose utilization by the different cell lines.
Abstract: Carbohydrate metabolism by four rat hepatoma cell lines in culture, namely, Reuber H35, MH1C1, RLC, and HTC, has been investigated. Glucose utilization by H35 and MH1C1 cells is lower than that by RLC and HTC cells. The four cell lines also differ with respect to the accumulation of lactic acid in the growth medium; in particular, H35 cells show uptake of lactic acid, rather than accumulation in the medium. Specific activities of a number of enzymes involved in glycolysis, gluconeogenesis, pentose phosphate pathway, and glycogen formation were determined in the four cell lines. A direct relationship between the differences was found for the activities of some enzymes belonging to carbohydrate metabolism, namely, hexokinase, pyruvate kinase, aldolases A and B, glucose-6-phosphate dehydrogenase, and phosphogluconate dehydrogenase and the differences found for glucose utilization by the different cell lines.
TL;DR: The conversion of U-labelled [14C]glucose-6-phosphate into other products by a soluble fraction of lysed spinach chloroplasts has been studied and it was found that both an oxidative pentose phosphate cycle and a glycolytic reaction sequence occur in this fraction.
Abstract: The conversion of U-labelled [14C]glucose-6-phosphate into other products by a soluble fraction of lysed spinach chloroplasts has been studied. It was found that both an oxidative pentose phosphate cycle and a glycolytic reaction sequence occur in this fraction. The formation of bisphosphates and of triose phosphates was ATP-dependent and occurred mainly via a glycolytic reaction sequence including a phosphofructokinase step. The conversion, of glucose-6-phosphate via the oxidative pentose phosphate cycle stopped with the formation of pentose monophosphates. This was found not to be because of a lack in transaldolase (or transketolase) activity, but because of the high concentration ratios of hexose monophosphate/pentose monophosphate used in our experiments for simulating the conditions in whole chloroplasts in the dark. Some regulatory properties of both the oxidative pentose phosphate cycle and of the glycolytic pathway were studied.
TL;DR: A striking decrease in the levels of Glc-1,6-P, in dystrophic muscle was found, which was associated with a marked reduction in the activity of phosphofructokinase, reflecting the pathological changes in glucose metabolism in the dyStrophic muscle.
TL;DR: C cerebral parameters tended to normalize, except for a further increase in alanine production with conversion of pyruvate into α-ketoglutarate available for the ammonia-detoxicating processes (amination to glutamate and amidation to glutamine).