[Biochemical changes taking place in the blood in the course of experimental acoustic stress. I. Fructosediphosphate aldolase].
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Acoustic Stimulation↗
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[Ratio of aldolase activity measured with fructosediphosphate and fructosemonophosphate in various organs and tissues of rats].
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Age Factors↗
[On the correlation fo fructosediphosphate and fructosemonophosphate aldolase activities in rat tissues under toxic conditions and starvation].
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Aldehyde-Lyases↗
An isozyme of erythrocyte pyruvate kinase (PK-Los Angeles) with impaired kinetics corrected by fructose-1, 6-diphosphate.
A mutant isozyme of erythrocyte pyruvate kinase was found in a family of French-Canadian ancestry in association with hemolytic anemia. The isozyme was characterized by normal maximal activity, pH optimum, heat stability, and fructosediphosphate activation constants, but had markedly reduced affinity for the substrate, phosphoenolpyruvate. This kinetic defect was corrected almost entirely in vitro by low concentrations of fructosediphosphate.
Anemia, Hemolytic, Congenital↗
Pyruvate kinase from human skeletal muscle.
A simple method is described for the isolation of crystalline pyruvate kinase from human skeletal muscle. The enzyme was purified by ammonium sulfate fractionation, heat treatment and crystallization. Two crystal forms of pyruvate kinase differing in solubility but not in specific activity were found. The homogenous enzyme preparations in triethanolamine buffer, pH 7.6 reveal at 25 degrees a specific activity of 245 U per mg protein, and of 340 U/mg in potassium phosphate buffer (50 mM). The enzyme is activated by inorganic phosphate and fructosediphosphate to the same extent, and inhibited non competetively by ammonium ion. The molecular weight as measured by gel filtration is 220,000 daltons and the enzyme molecule is composed of 4 subunits.
Chromatography, Gel↗
Fermentation of pectin and glucose, and activity of pectin-degrading enzymes in the rumen bacterium Lachnospira multiparus.
AIMS: Lachnospira multiparus belongs to the main rumen pectinolytic bacteria. Its carbohydrate metabolism was studied in growth experiments on laboratory fermenters, and using assays of activities of enzymes involved in pectin fermentation. METHODS AND RESULTS: The type strain of this species and two substrates were used. Lachnospira multiparus ATCC 19207 grew on pectin and glucose at a similar rate and had no preference for one or the other substrate. Pectin-grown cultures, however, produced significantly more acetate and less formate, lactate, ethanol, hydrogen, cell dry matter and protein than corresponding cultures grown on glucose. Extracellular exopectate lyase (EC 4.2.2.9) was the principal enzyme degrading the pectin macromolecule. Cell extracts possessed 2-keto-3- deoxy-6-phosphogluconate aldolase (EC 4.1.2.14) and fructosediphosphate aldolase (EC 4.1.2.13) activity. The former enzyme catalyses the final reaction in the Entner-Doudoroff pathway; the latter is the key enzyme of glycolysis and the pentose phosphate pathway. CONCLUSION: These results are consistent with the assumption that acidic products of pectin degradation are catabolized via a modified Entner-Doudoroff pathway. Phosphogluconate was not metabolized by cell extracts of the strain studied. SIGNIFICANCE AND IMPACT OF THE STUDY: This suggests that the conventional Entner-Doudoroff pathway of glucose utilization does not operate in this bacterium, presumably because of the lack of 6-phosphogluconate dehydrase (EC 4.2.1.12) activity.
Animals↗
Comparative intermediary metabolism of vegetative cells and microcysts of Myxococcus xanthus.
Crude extracts of both vegetative cells and glycerol-induced microcysts of Myxococcus xanthus contained the following enzyme activities: phosphofructokinase, phosphoglucoisomerase, fructose-1,6-diphosphatase, fructosediphosphate aldolase, glyceraldehyde-3-phosphate dehydrogenase, phosphopyruvate carboxylase, citrate synthase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, malate dehydrogenase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, phosphoglucomutase, and uridine diphosphate glucose pyrophosphorylase. With the exception of isocitrate dehydrogenase, which was present at a fivefold higher concentration in microcysts, all activities in extracts from both types of cells were essentially equal. Hexokinase and pyruvate kinase could not be detected in extracts from either type of cell. Microcysts metabolized acetate at a lower rate than did vegetative cells. Most of this decrease was reflected in a substantial decrease in ability of microcysts to oxidize acetate to CO(2). In addition, microcysts and vegetative cells showed a different distribution of (14)C-label from incorporated acetate.
Acetates↗
[Comparative evaluation of the protective effect of sodium valproate, phenazepam and ionol in stress-induced liver damage in rats].
Ionol, a synthetic antioxidant, limits the stressor liver injury to a greater extent than sodium, valproate and phenazepam, activators of a GABA-ergic link of the stress-limiting organism systems. This injury is exhibited in the organospecific elevated levels of blood enzymes fructosediphosphate aldolase depression of N-demethylase activity of microsomal monooxygenases and a decrease in the amount of cytochromes P-450 and B5.
Animals↗
[Pyrivate kinase deficiency. II. Biochemical studies (author's transl)].
Pyruvate kinase deficiency was studied biochemically in ten homozygous and seven heterozygous individuals who previously had been examined clinically and hematologically (see part I). In crude hemolysates some properties of the deficient enzymes were found to be altered. The pH optimum was shifted towards the alkaline range, and the thermal optimum was found between 17 and 27 degrees Cinstead of between 37 und 47 degrees C. The abnormal enzymes were much less stable than normal pyruvate Kinase (PK), and more susceptible to inhibition by adenosinetriphosphate. The affinity to adenosinediphosphate was normal in all cases whereas the affinity to phosphoenolpyruvate was either normal (two cases/, increased (two cases) or slightly decreased (six cases). Fructosediphosphate activated the abnormal enzymes by a factor of 1.5--18 and simultaneously transformed the sigmoidal affinity curve with phosphoenolpyruvate into the hyperbolic curve known for the normal enzyme. The consumption of glucose and the formation of lactate were higher in PK deficient erythrocytes than in normal cells but lower than in erythrocyte populations with similar reticulocyte counts. The formation of 2,3-diphosphoglycerate was markedly increased, whereas its breakdown was low. A close relation between the degree of reticulocytosis and the impairment of glucose metabolism was found. In patients with high reticulocyte counts, i.e. in the splenectomized patients, the highest concentrations of glucose-6-phosphate, phosphoenolpyruvate, 3-phosphoglycerate and 2,3-diphosphoglycerate as well as a high formation and a low breakdown of 2,3-diphosphoglycerate and a deficit in lactate formation were found. In heterozygotes, small increases of the concentration of glucose-6-phosphate, phosphoenolpyruvate and 3-phosphoglycerate were demonstrated. Our results support the conclusion that PK deficiency is mainly a disorder of the reticulocytes. Their metabolism grossly deteriorates within the venous sinuses of the spleen. Splenectomy improves the clinical course because this critical area of microcirculation with a highly unfavourable metabolic milieu is eliminated.
Anemia, Hemolytic, Congenital↗
[Splitting of fructose diphosphate by muscle and tumor homogenates].
Effect of MgCl2 and ATP on the elevation in lactate, pyruvate and methylglyoxale content was studied on incubation of fructosediphosphate with muscle and tumor homogenates. Muscle homogenate accumulated lactate, pyruvate and methyglyoxale more intensively as compared with tumor homogenate. Pyruvate was formed only in presence of MgCl2 and ATP, although it did not practically affect the elevation of lactate in muscle homogenate. The data obtained suggest that tumor homogenate does not contain the enzymatic system involved in methylglyoxale formation.
Adenosine Triphosphate↗
A potential role of the cytoskeleton of Saccharomyces cerevisiae in a functional organization of glycolytic enzymes.
Numerous individual enzymes participate in a given synthetic or degradative pathway in which the product of one reaction becomes the substrate for the subsequent enzyme. This raises the question of whether the product of one 'soluble' enzyme diffuses freely through the available cell volume, where it accidentally collides with the subsequent 'soluble' enzyme. Alternatively, enzymes acting in a given pathway may be organized in ordered structures, metabolons. Certain glycolytic enzymes have been shown to co-localize with the cytoskeleton in mammalian cells. We deleted genes coding for proteins associated with the cytoskeleton of Saccharomyces cerevisiae: TPM1 coding for tropomyosin, SAC6 for fimbrin and CIN1 for a microtubule-associated protein. Single deletions or deletions of two such genes had no effect on the specific activities of glycolytic enzymes, or on the rates of glucose consumption and ethanol production. However, the concentrations of glycolytic metabolites during a switch from a gluconeogenic mode of metabolism, growth on an ethanol medium, to glycolysis after glucose addition showed transient deviations from the normal change in metabolite concentrations, as observed in wild type cells. However, all metabolites in mutant strains reached wild-type levels within 2-4 h after the shift. Only ATP levels remained low in all but the tmp1-Delta-sac6-Delta double mutant strains. These observations can be interpreted to mean that metabolic reorganization from a gluconeogenic to a glycolytic metabolism is facilitated by an intact cytoskeleton in yeast.
Adenosine Triphosphate↗
Effect of high-energy phosphates and free radical scavengers on replant survival in an ischemic extremity model.
In replantation surgery, preoperative and intraoperative ischemia can lead to irreversible changes that prevent reperfusion during the subsequent re-establishment of circulation. These changes are termed the no-reflow phenomenon. Ischemic phase damage was addressed by comparing the dose-response effects of controls vs. five different high-energy phosphate compounds on replanted limb survival. Reperfusion damage was evaluated via comparisons of controls with superoxide dismutase (SOD). Ischemic hindlimbs treated with high-energy phosphates displayed improved survival compared with controls. Limbs treated with SOD demonstrated no change in survival at 4 hours and improved survival at 8 hours. Combining adenosine and SOD had no improved effect on survival. Adenosine was the most effective high-energy phosphate in limiting ischemic damage. The free radical scavenger (SOD) was beneficial only at the later stages of ischemia. In this experimental model, there appears to be a role for both phosphates and free radical scavengers in enhancing ischemic tissue survival.
Adenosine↗
Biochemical characterization of three mutant isozymes of erythrocyte pyruvate kinase: PK-"Gainesville," PK-"San Juan," and PK-"Cape Canaveral".
Pyruvate kinase was partially purified from erythrocytes of three unrelated, nonconsaguineous patients with chronic hemolytic anemia of differing clinical severities. Characterization of the defective PK isozymes by internationally standardized criteria indicated that one (PK-"Gainesville") had severely impaired substrate affinity, another (PK-"San Juan") had markedly reduced residual activity, and the third (PK-"Cape Canaveral") had a combination of milder defects. Each appears representative of subsets emerging from the heterogeneous molecular defects that make up pyruvate kinase deficiency.
Adenosine Triphosphate↗
Fructose-2,6-bisphosphate and control of carbohydrate metabolism in eukaryotes.
Fructose-2,6-bisphosphate is an important intracellular biofactor in the control of carbohydrate metabolic fluxes in eukaryotes. It is generated from ATP and fructose-6-phosphate by 6-phosphofructo-2-kinase and degraded to fructose-6-phosphate and phosphate ion by fructose-2,6-bisphosphatase. In most organisms these enzymatic activities are contained in a single polypeptide. The reciprocal modulation of the kinase and bisphosphatase activities by post-translational modifications places the level of the biofactor under the control of extra-cellular signals. In general, these signals are generated in response to changing nutritional states, therefore, fructose-2,6-bisphosphate plays a role in the adaptation of organisms, and the tissues within them, to changes in environmental and metabolic states. Although the specific mechanism of fructose-2,6-bisphosphate action varies between species and between tissues, most involve the allosteric activation of 6-phosphofructo-1-kinase and inhibition of fructose-1,6-bisphosphatase. These highly conserved enzymes regulate the fructose-6-phosphate/fructose-1,6-bisphosphate cycle, and thereby, determine the carbon flux. It is by reciprocal modulation of these activities that fructose-2,6-bisphosphate plays a fundamental role in eukaryotic carbohydrate metabolism.
Animals↗
Pyruvate kinase activity and response to allosteric effectors in rat erythrocytes and reticulocytes fractionated by multiple partitioning in aqueous two-phase systems.
Specific activity of pyruvate kinase decreases as the age of rat erythrocytes increases in fractions obtained by counter-current distribution in dextran-polyethylene glycol biphasic systems; the enzyme is inhibited by ATP and activated by fructose-1,6-bisphosphate at low phosphoenol pyruvate concentrations. Specific activity does not change in fractions from greater than 95 per cent-rich reticulocytes (anaemic rats); the enzyme is inhibited by ATP but not activated by fructose-1,6-bisphosphate. These results can be explained on the basis of different pyruvate kinase isozymes and suggest that decrease in activity is not affecting regulatory properties during erythrocytes aging.
Adenosine Triphosphate↗
Some effects of fructose-1,6-diphosphate on rat myocardial tissue related to a membrane-stabilizing action.
This study aims at elucidating the mechanism of action of extracellular fructose-1,6-diphosphate (FDP). FDP is able to inhibit Ca++ entry into the myocardial tissue with an IC50 value of 11.5 mM and in addition, it is bound by rat heart slices, the binding being activated by Zn and conditions of chemical hypoxia induced by KCN and iodoacetate. The overall effect of extracellular FDP includes an increase of frequency and amplitude of contraction of perfused heart at concentration below 1 mM, and, in general, a stimulation of the oxygen consumption of the tissue. The antihaemolytic effect of FDP suggests its action as a membrane stabilizer. The effects of extracellular FDP on the myocardial cell can be interpreted both on the basis of a limited permeability of the cell membrane to it and as a purely extracellular effect transduced through the cell membrane with a final response consisting of an increase in the intracellular FDP.
Animals↗
Studies of the regulation of renal gluconeogenesis in normal and Pi depleted proximal tubule cells.
Pi depletion of proximal tubule cells isolated from mouse kidney results in a decrease in the cell content of fructose-2,6-bisphosphate and an increase in the rate of gluconeogenesis from pyruvate, malate and succinate. Gluconeogenesis from glycerol is unaffected by Pi depletion. Introduction of fructose-2,6-bisphosphate into the cytosol of ATP-permeabilized cells is accompanied by a fall in gluconeogenesis. The presence of external Ca2+ stimulates gluconeogenesis. When cytosolic Ca2+ is raised to 1.8 microM by permeabilization, the resealed cells still require 2.5 mM Ca2+ in the bathing medium in order to perform gluconeogenesis at the maximum rate. Cells permeabilized in the presence of cAMP show a decreased rate of glucose production. Phorbol ester stimulates gluconeogenesis provided that the phorbol treatment is performed in the absence of Ca2+ ions. It is suggested that Pi depletion may stimulate pyruvate carboxylase activity and facilitate the entry of certain gluconeogenic substrates into mitochondria. It is also proposed that important aspects of the control of renal gluconeogenesis by parathyroid hormone are mediated by protein kinase C.
Animals↗