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E A Newsholme

Publications and source records attributed to E A Newsholme.

At least 19 recordsLinked to original sources
PubMed1979

Activities of enzymes of fat and ketone-body metabolism and effects of starvation on blood concentrations of glucose and fat fuels in teleost and elasmobranch fish.

1. Activities of 3-oxo acid CoA-transferase and carnitine palmitoyltransferase together with tri- and di-acylglycerol lipase were present in red and heart muscles of the teleost fish. However, d-3-hydroxybutyrate dehydrogenase activity was not detectable. These results suggest that the heart and red muscles of the teleosts should be able to utilize the fat fuels triacylglycerol, fatty acids or acetoacetate, but not hydroxybutyrate. The muscles from the elasmobranchs differed in that d-3-hydroxybutyrate dehydrogenase and 3-oxo acid CoA-transferase activities were present, but carnitine palmitoyltransferase activity was not detectable. This suggests that ketone bodies are the most important fat fuels in elasmobranchs. 2. The concentrations of acetoacetate, 3-hydroxybutyrate, glycerol, non-esterified fatty acids and triacylglycerols were measured in blood or plasma of several species of fish (teleosts and elasmobranchs) in the fed state. Teleosts have a 10-fold higher concentration of plasma non-esterified fatty acids, but a lower blood concentration of ketone bodies; both acetoacetate and 3-hydroxybutyrate are present in blood of elasmobranchs, whereas 3-hydroxybutyrate is absent from that of the teleosts. 3. The effects of starvation (up to 150 days) on the concentrations of blood metabolites were studied in a teleost (bass) and an elasmobranch (dogfish). In the bass there was a 60% decrease in blood glucose after 100 and 150 days starvation. In dogfish there was a large increase in the concentration of ketone bodies, whereas in bass the concentration of acetoacetate (the only ketone body present) remained low (<0.04mm) throughout the period of starvation. The concentration of plasma non-esterified fatty acids increased in bass, but decreased in dogfish. These changes are consistent with the predictions based on the enzyme-activity data. 4. Starvation did not change the activities of ketone-body-utilizing enzymes or that of phosphoenolpyruvate carboxykinase in heart and red skeletal muscles of both fish, but it decreased markedly the activity of phosphoenolpyruvate carboxykinase in white skeletal muscle of both fish. However, in the liver of the dogfish, starvation resulted in a twofold increase in the activities of 3-hydroxybutyrate dehydrogenase and acetoacetyl-CoA thiolase, whereas in bass liver it decreased the activity of acetoacetyl-CoA thiolase and increased that of 3-oxo acid CoA-transferase. The activity of phosphoenolpyruvate carboxykinase was increased twofold in the liver of bass, but was unchanged in that of the dogfish. 5. The difference in changes in concentrations of blood metabolites and enzyme activities in the two fish support the suggestion that, in starvation, ketone bodies, but not non-esterified fatty acids, are an important fuel for muscle in elasmobranchs, whereas non-esterified fatty acids, but not ketone bodies, are an important fuel in teleosts. The results are discussed in relation to the evolution of a discrete lipid-storing adipose tissue in teleosts and higher vertebrates.

Animals↗
PubMed1979

Sensitivity of glucose uptake and lipolysis of white adipocytes of the rat to insulin and effects of some metabolites.

1. Insulin increased glucose uptake and inhibited lipolysis in white adipocytes of the rat over the same concentration range of the hormone: the half-maximal effects were observed at approx. 10 microunits of insulin/ml. Thus, contrary to previous reports, no difference in sensitivity of the two processes to insulin could be found, which suggests that both these effects of insulin are important in increasing the rate of glucose utilization after a meal. 2. Adenosine deaminase, which lowers the concentration of adenosine in the incubation medium, decreased the sensitivity of both processes (lipolysis and glucose uptake) to insulin: this suggests that adenosine increases the sensitivity of both processes. Similarly, lactate and 3-hydroxybutyrate increased the sensitivity of both processes (to the same extent) to insulin. It is suggested that this increased sensitivity will improve the response (of adipose tissue) to insulin on refeeding after a prolonged period of starvation (when the hydroxybutyrate concentration is high), and after a short burst of exercise, when the blood lactate concentration is high and when large amounts of glucose are produced from lactate via gluconeogenesis in the liver.

Adenosine Deaminase↗
PubMed1979

Changes in the contents of adenine nucleotides and intermediates of glycolysis and the citric acid cycle in flight muscle of the locust upon flight and their relationship to the control of the cycle.

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.

Adenine Nucleotides↗
PubMed1979

Use of enzyme activities as indices of maximum rates of fuel utilization.

It can be shown theoretically and experimentally that the maximum activities in vitro of enzymes that catalyse near-equilibrium reactions in vivo must be considerably higher than the maximum flux through that pathway. Consequently, the activities of such enzymes cannot provide quantitative information on the maximum possible flux through a pathway. On the other hand, the maximum activity of an enzyme that catalyses a non-equilibrium reaction in vivo may provide quantitative information. Such possibilities must be tested experimentally. Thus the maximum flux through a given metabolic pathway is measured (or calculated) and compared with the maximum in vitro activities of enzymes that catalyse non-equilibrium reactions in that pathway. Catalytic activities similar to the flux suggest that such enzymes may be useful as flux indicators. For example, phosphorylase or phosphofructokinase activities provide a quantitative indication of maximum flux through glycolysis-from-glycogen (i.e. anaerobic glycolysis); hexokinase activities provide a quantitative indication of maximum flux through glycolysis-from-glucose; 2-oxoglutarate dehydrogenase activities provide a quantitative indication of maximum flux through the citric acid cycle. The advamtages of the use of enzyme activities in this manner include simplicity, general applicability to pathways, tissues and animals, and minimum intervention (particularly in larger animals including the human species). One disadvantage is that the properties of the enzyme must be known in detail before an assay that gives maximum activities can be developed, and the properties of enzymes that catalyse non-equilibrium reactions may be complex. These considerations emphasize the dangers of quantitative interpretation of the maximum flux through pathways from 'near-equilibrium' enzymes or from 'non-equilibrium' enzymes whose properties have been inadequately studied.

Adenosine Triphosphate↗
PubMed1978

The role of phosphoenolpyruvate carboxykinase in amino acid metabolism in muscle.

Starvation or feeding rats on a high-protein diet, valine or isoleucine, but not leucine, increases the activity of muscle phosphoenolpyruvate carboxykinase, but has no effect on NADP+-linked malate dehydrogenase. This suggests that muscle phosphoenolpyruvate carboxykinase is involved in oxidation or conversion of some amino acids to alanine.

Amino Acids↗
PubMed1978

Activities and some properties of 5'-nucleotidase, adenosine kinase and adenosine deaminase in tissues from vertebrates and invertebrates in relation to the control of the concentration and the physiological role of adenosine.

1. The maximal activities of 5'-nucleotidase, adenosine kinase and adenosine deaminase together with the Km values for their respective substrates were measured in muscle, nervous tissue and liver from a large range of animals to provide information on the mechanism of control of adenosine concentration in the tissues. 2. Detailed evidence that the methods used were optimal for the extraction and assay of these enzymes has been deposited as Supplementary Publication SUP 50088 (16pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K.,from whom copies can be obtained on the terms indicated in Biochem. J. (1978), 169, 5. This evidence includes the effects of pH and temperature on the activities of the enzymes. 3. In many tissues, the activities of 5'-nucleotidase were considerably higher than the sum of the activities of adenosine kinase and deaminase, which suggests that the activity of the nucleotidase must be markedly inhibited in vivo so that adenosine does not accumulate. In the tissues in which comparison is possible, the Km of the nucleotidase is higher than the AMP content of the tissue, and since some of the latter may be bound within the cell, the low concentration of substrate may, in part, be responsible for a low activity in vivo. 4. In most tissues and animals investigated, the values of the Km of adenosine kinase for adenosine are between one and two orders of magnitude lower than those for the deaminase. It is suggested that 5'-nucleotidase and adenosine kinase are simultaneously active so that a substrate cycle between AMP and adenosine is produced: the difference in Km values between kinase and deaminase indicates that, via the cycle, small changes in activity of kinase or nucleotidase produce large changes in adenosine concentration. 5. The activities of adenosine kinase or deaminase from vertebrate muscles are inversely correlated with the activities of phosphorylase in these muscles. Since the magnitude of the latter activities are indicative of the anaerobic nature of muscles, this negative correlation supports the hypothesis that an important role of adenosine is the regulation of blood flow in the aerobic muscles.

Adenosine↗
PubMed1978

Properties of pyruvate kinase and phosphoenolpyruvate carboxykinase in relation to the direction and regulation of phosphoenolpyruvate metabolism in muscles of the frog and marine invertebrates.

1. The properties of pyruvate kinase and, if present, phosphoenolpyruvate carboxykinase from the muscles of the sea anemone, scallop, oyster, crab, lobster and frog were investigated. 2. In general, the properties of pyruvate kinase from all muscles were similar, except for those of the enzyme from the oyster (adductor muscle); the pH optima were between 7.1 and 7.4, whereas that for oyster was 8.2; fructose bisphosphate lowered the optimum pH of the oyster enzyme from 8.2 to 7.1, but it had no effect on the enzymes from other muscles. Hill coefficients for the effect of the concentration of phosphoenolpyruvate were close to unity in the absence of added alanine for the enzymes from all muscles except oyster adductor muscle; it was 1.5 for this enzyme. Alanine inhibited the enzyme from all muscles except the frog; this inhibition was relieved by fructose bisphosphate. Low concentrations of alanine were very effective with the enzyme from the oyster (50% inhibition was observed at 0.4mm). Fructose bisphosphate activated the enzyme from all muscles, but extremely low concentrations were effective with the oyster enzyme (0.13mum produced 50% activation). 3. In general, the properties of phosphoenolpyruvate carboxykinase from the sea anemone and oyster muscles are similar: the K(m) values for phosphoenolpyruvate are low (0.10 and 0.13mm); the enzymes require Mn(2+) in addition to Mg(2+) for activity; and ITP inhibits the enzymes and the inhibition is relieved by alanine. These latter compounds had no effect on enzymes from other muscles. 4. It is suggested that changes in concentrations of fructose bisphosphate, alanine and ITP produce a coordinated mechanism of control of the activities of pyruvate kinase and phosphoenolpyruvate carboxykinase in the sea anemone and oyster muscles, which ensures that phosphoenolpyruvate is converted into oxaloacetate and then into succinate in these muscles under anaerobic conditions. 5. It is suggested that in the muscles of the crab, lobster and frog, phosphoenolpyruvate carboxykinase catalyses the conversion of oxaloacetate into phosphoenolpyruvate. This may be part of a pathway for the oxidation of some amino acids in these muscles.

Alanine↗
PubMed1978

Maximum activities and effects of fructose bisphosphate on pyruvate kinase from muscles of vertebrates and invertebrates in relation to the control of glycolysis.

1. Comparison of the maximum activities of pyruvate kinase with those of phosphofructokinase in a large number of muscles from invertebrates and vertebrates indicates that, in general, in any individual muscle, the activity of pyruvate kinase is only severalfold higher than that of phosphofructokinase. This is consistent with the suggestion, based on mass-action ratio data, that the pyruvate kinase reaction is non-equilibrium in muscle. However, the range of activities of pyruvate kinase in these muscles is considerably larger than that of phosphofructokinase. This difference almost disappears if the enzyme activities from muscles that are known to possess an anaerobic ;succinate pathway' are excluded. It is suggested that, in these muscles, phosphofructokinase provides glycolytic residues for both pyruvate kinase (i.e. glycolysis) and phosphoenolpyruvate carboxykinase (i.e. the succinate pathway). This is supported by a negative correlation between the activity ratio, pyruvate kinase/phosphofructokinase, and the activities of nucleoside diphosphokinase in these muscles, since high activities of nucleoside diphosphokinase are considered to indicate the presence of the succinate pathway. 2. The effect of fructose bisphosphate on the activities of pyruvate kinase from many different muscles was studied. The stimulatory effect of fructose bisphosphate appears to be lost whenever an efficient system for supply of oxygen to the muscles is developed (e.g. insects, squids, birds and mammals). This suggests that activation of pyruvate kinase is important in the co-ordinated regulation of glycolysis in anaerobic or hypoxic conditions, when the change in glycolytic flux during the transition from rest to activity needs to be large in order to provide sufficient energy for the contractile activity. However, lack of this effect in the anaerobic muscles of the birds and mammals suggests that another metabolic control may exist for avian and mammalian pyruvate kinase in these muscles.

Animals↗
PubMed1978

The role of creatine kinase and arginine kinase in muscle.

Arginine and creatine kinase activities in different muscles are compared with calculated maximum rates of ATP turnover. The magnitude of the kinase activities decreases in the following order: anaerobic muscles and vertebrate skeletal muscles greater than heart muscle greater than insect flight muscle. The maximum activity of phosphagen kinases (i.e. creatine kinase and arginine kinase), in the direction of phosphagen formation, is lower than the calculated maximum rate of ATP turnover in insect flight muscle or rat heart.

Adenosine Triphosphate↗