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At least 19 recordsLinked to original sources
PubMed1979

Microelectrophoretic application of metabolic modifiers of the phosphofructokinase-hexosediphosphatase-system onto various types of bulbar respiratory neurons.

Three metabolic modifiers of the PFK-HDPase system were applied to bulbar respiratory neurons and, for comparison, also to unspecific cells. F-6-P did not alter the spike density of the majority of the respiratory and about half of the unspecific neurons. When responding, IE units were activated and unspecific cells were inhibited. Citrate did not alter the spike density of about half of all neurons tested. When responding, excitation prevailed in IE and E units, while unspecific cells were inhibited. AMP did not alter the spike density of the majority of the respiratory and about half of the unspecific cells. When responding, I neurons were activated, inhibition preponderated in IE units and both effects occurred in unspecific cells. The large number of zero effects suggests that the activity of only part of the cells is governed by the PFK-HDPase system.

Adenosine Monophosphate↗
PubMed1975

On the activity and regulation of anaplerotic and gluconeogenetic enzymes during the growth process of baker's yeast. The biphasic growth.

The anaplerotic and gluconeogenetic metabolism of baker's yeast was studied at the enzymatic level during glucose-ethanol diauxic growth in the presence and absence of aspartate. Of the two possible anaplerotic systems, only the pyruvate carboxylase by-pass was present during the whole growth process. The second system, the glyoxylate by-pass (isocitrate lyase as the indicator), like the specific enzymes of the gluconeogenetic metabolism, phosphoenolpyruvate carboxykinase and hexosediphosphatase began to appear only after the glucose had been consumed. The addition of glucose during the growth phase based on ethanol effected a rapid disappearance of phosphoenolpyruvate carboxykinase and hexosediphosphatase activities. The activity of pyruvate carboxylase decreased when the growth medium was supplied with asparate. The presence of aspartate had no effect on the activities of the other enzymes studied.

Aerobiosis↗
PubMed1968

Enzymes of fructose metabolism in human liver.

The enzyme activities involved in fructose metabolism were measured in samples of human liver. On the basis of U/g of wet-weight the following results were found: ketohexokinase, 1.23; aldolase (substrate, fructose-1-phosphate), 2.08; aldolase (substrate, fructose-1,6-diphosphate), 3.46; triokinase, 2.07; aldehyde dehydrogenase (substrate, D-glyceraldehyde), 1.04; D-glycerate kinase, 0.13; alcohol dehydrogenase (nicotinamide adenine dinucleotide [NAD]) substrate, D-glyceraldehyde), 3.1; alcohol dehydrogenase (nicotinamide adenine dinucleotide phosphate [NADP]) (substrate, D-glyceraldehyde), 3.6; and glycerol kinase, 0.62. Sorbitol dehydrogenases (25.0 U/g), hexosediphosphatase (4.06 U/g), hexokinase (0.23 U/g), and glucokinase (0.08 U/g) were also measured. Comparing these results with those of the rat liver it becomes clear that the activities of alcohol dehydrogenases (NAD and NADP) in rat liver are higher than those in human liver, and that the values of ketohexokinase, sorbitol dehydrogenases, and hexosediphosphatase in human liver are lower than those values found in rat liver. Human liver contains only traces of glycerate kinase. The rate of fructose uptake from the blood, as described by other investigators, can be based on the activity of ketohexokinase reported in the present paper. In human liver, ketohexokinase is present in a four-fold activity of glucokinase and hexokinase. This result may explain the well-known fact that fructose is metabolized faster than glucose.

Alcohol Oxidoreductases↗
PubMed1973

Regulation of glucose synthesis in hormone-sensitive isolated rat hepatocytes.

A simplified procedure was developed for isolation of intact, hormone-sensitive liver cells in a high and reproducible yield. These cells produce glucose from various precursors at rates comparable to those achieved in isolated perfused liver. Glucagon enhanced glucose synthesis from pyruvate, dihydroxyacetone, fructose, or xylitol more effectively at low than at high substrate concentration. At high pyruvate concentrations (>2 mM), glucagon or adenosine 3':5'-cyclic monophosphate (0.1 mM) exerts a curious inhibition of gluconeogenesis that can be reverted to stimulation on addition of ethanol. It is suggested that glucagon and cyclic AMP inhibit pyruvate dehydrogenase and thus limit the supply of reducing equivalents needed for glucose formation. Supporting evidence for hormonal control of pyruvate dehydrogenase in isolated liver cells is provided by the fact that glucagon decreases and insulin increases decarboxylation of [1-(14)C]pyruvate. Calcium salts (1.3 mM) enhance glucose formation from pyruvate but greatly enhance the inhibition exerted by the divalent cationophore, A23187. Inhibition by glucagon of glucose synthesis from pyruvate is additive with the effects of A23187 + Ca(++). However, with dihydroxyacetone as substrate, glucagon partially reverses the inhibition exerted by A23187 + Ca(++). The results are consistent with glucagon effecting an inhibition of pyruvate dehydrogenase and a stimulation of hexosediphosphatase activities.

Acetone↗
PubMed1979

Catabolite inactivation of gluconeogenic enzymes in mutants of yeast deficient in proteinase B.

Strains of Saccharomyces cerevisiae bearing nonsense mutations in the structural gene for proteinase B (EC 3.4.22.9) have been examined for the ability to make the transition from growth on acetate to growth on glucose and for the ability to inactivate three glucoeogenic enzymes during the transition because proteinase B has been proposed by others to be responsible for the inactivation of the three enzymes during the growth transition. The mutant strains make the growth transition normally. Catabolite inactivation of hexosediphosphatase (D-fructose-1,6-biphosphate 1-phosphohydrolase, EC 3.1.3.11), malate dehydrogenase (L-malate:NAD+ oxidoreductase, EC 1.1.1.37), and phosphoenolpyruvate carboxykinase (ATP) [ATP:oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.49] occurred in prb1 mutants with kinetics similar to those seen in wild-type strains. We infer that proteinase B activity is not essential for the process of catabolite inactivation.

Fructose-Bisphosphatase↗
PubMed1974

Persistence of cadmium-induced metabolic changes in liver and kidney.

Daily intraperitoneal injection of cadmium chloride (1 milligram per kilogram) for 45 days enhanced gluconeogenesis as evidenced by significant increases in the activities of liver and kidney cortex pyruvate carboxylase, phosphopyruvate carboxylase, hexosediphosphatase, and glucose-6-phosphatase, the quartet of key, rate-limiting enzymes involved in the biotransformation of noncarbohydrate precursors into glucose. Whereas cadmium treatment decreased the level of hepatic glycogen, the concentration of blood glucose and urea was significantly elevated by this heavy metal. Discontinuation of the heavy metal treatment for 28 days, in rats previously injected with cadmium for 45 days, failed to restore the observed biochemical alterations in hepatic and renal carbohydrate metabolism to control values. Evidence indicates that cadmium augments the glucose-synthesizing capacity of liver and kidney cortex and that various metabolic changes persist even after a 4-week period of withdrawal from exposure to the heavy metal.

Animals↗
PubMed1968

Metabolism of carbohydrates by Pasteurella pseudotuberculosis.

Cell-free extracts of Pasteurella pseudotuberculosis and P. pestis catalyzed a rapid and reversible exchange of electrons between pyridine nucleotides. Although the extent of this exchange approximated that promoted by the soluble nicotinamide adenine dinucleotide (phosphate) transhydrogenase of Pseudomonas fluorescens, the reaction in the pasteurellae was associated with a particulate fraction and was not influenced by adenosine-2'-monophosphate. The ability of P. pseudotuberculosis to utilize this system for the maintenance of a large pool of nicotinamide adenine dinucleotide phosphate could not be correlated with significant participation of the Entner-Doudoroff path or catabolic use of the hexose-monophosphate path during metabolism of glucose. As judged by the distribution of radioactivity in metabolic pyruvate, glucose and gluconate were fermented via the Embden-Meyerhof and Entner-Doudoroff paths, respectively. With the exception of hexosediphosphatase, all enzymes of the three paths were detected, although little or no gluconokinase or phosphogluconate dehydrase was present unless the organisms were cultivated with gluconate. The significance of these findings is discussed with respect to the regulation of carbohydrate metabolism in the pasteurellae, related enteric bacteria, and P. fluorescens.

Carbon Isotopes↗