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At least 19 recordsLinked to original sources
PubMedDate not supplied

[Content of the nonsaponifying substances in crystalline fructosediphosphate aldolase from the muscles of rabbits normally and in atherosclerosis].

The non-saponifying fraction was found in highly purified crystalline preparations of fructose diphosphate aldolase (EC 4.1.2.13). The amount of the non-saponifying substance in the aldolase of intact animals is different and depends not only on the degree of the enzyme purification. In the experiments when the non-saponifying residue was added to the incubation mixture it was found to produce no effect on the aldolase activity with the presence of fructose-1,6-diphosphate and fructose-1-phosphate. A decrease is observed in the activity of the crystalline preparations during their storage for four months which depends directly on the amount of the non-saponifying fraction in these preparations. The amount of the non-saponifying fraction in equally purified preparations of aldolase with experimental atherosclerosis is twice as low as compared to the norm. The non-saponifying residues of the fructose-diphosphate aldolase muscular preparations in the norm and with experimental atherosclerosis consist of two components, one of them being cholesterol, the chemical nature of the other component is not the same in the norm and with atherosclerosis.

Animals↗
PubMed1975

[Study of the fructosediphosphate aldolase and transketolase activity in the nystatin producer, Actinomyces noursei].

Activity of transketolase, an enzyme of the pentose cycle and fructosodiphosphataldolase, an enzyme of glycolisis was studied in the dynamics of development of the nystatin-producing organism and its inactive mutant under various conditions of their cultivation with a purpose of finding relation between the antibiotic production and general metabolism of Act. noursei. The transketolase activity of the organism was 2-4 times higher than that of the inactive mutant. Addition of 8000 Units/ml of nystatin to the medium markedly suppressed (50-100 per cent) the aldolase activity, however it had no effect on the transkelotase activity. Possibly the antibiotic accumulated in the mycelium played the role of a regulator of the activity of the enzymes, directing the metabolites along the hexosomonophosphate pathway of carbohydrate dissimilation.

Aerobiosis↗
PubMed1977

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↗
PubMed1975

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↗
PubMedDate not supplied

[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↗
PubMed1977

[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↗
PubMedDate not supplied

[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↗
PubMed1992

Effect of galactosamine on hepatic carbohydrate metabolism: protective role of fructose 1,6-bisphosphate.

Intraperitoneal administration of galactosamine (400 mg/kg body wt) to rats results in reversible liver cell injury that is related to a dose-dependent depletion of uridine phosphates by formation of UDP-sugar derivatives. This damage was monitored through changes in serum enzymatic activities that increased after the first 6 hr of drug administration. Glycemia and serum albumin remained stable during liver injury, whereas cholesterol and triglycerides decreased. To maintain plasma glucose concentration, the hepatic carbohydrate metabolism was greatly altered. Glycogen dropped during the first hours, remaining low for up to 48 hr. Fructose 2,6-bisphosphate and ATP levels decreased even faster than glycogen, with lactate following a similar diminution and being restored in parallel with both metabolites. The reduction in fructose 2,6-bisphosphate can be explained by changes in the substrates or modulators of the 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase, because neither the cyclic AMP levels nor the activity ratio of the enzyme were modified. Simultaneous administration of galactosamine and fructose 1,6-bisphosphate (2 gm/kg) prevented liver cell death, as monitored by serum enzyme activities. Furthermore, the bisphosphorylated metabolite had protective effects on the changes in liver calcium content and ATP and fructose 2,6-bisphosphate concentrations. In contrast, fructose, fructose-1-phosphate and fructose-6-phosphate had no significant protection. Fructose 1,6-bisphosphate might decrease galactosamine toxicity by increasing fructose 2,6-bisphosphate and ATP levels, the changes in both metabolites probably being related. The significance of these findings with respect to the mechanism of galactosamine-induced liver injury is also discussed.

Adenosine Triphosphate↗
PubMed1992

Isoenzymes of carbohydrate metabolism in primary cultures of hepatocytes from thioacetamide-induced rat liver necrosis: responses to growth factors.

Hepatocytes isolated from the liver of rats after a necrotizing dose of thioacetamide (6.6 mmol/kg) were used to study the postnecrotic process of liver regeneration. Flow cytometry analysis revealed populations of dedifferentiated hepatocytes exhibiting physical properties (size and fluorescence emission at 530 nm) similar to those found in fetal (22 days old) liver cells. The percentage of these cells increased progressively from 24 to 48 and 72 hr after thioacetamide administration. In primary cultures of hepatocytes the effects of phorbol 12-myristate 13-acetate, bombesin and insulin were investigated on the 6-phosphofructo 2-kinase/fructose 2,6 bisphosphate system. Bombesin and insulin stimulated 6-phosphofructo 2-kinase activity and fructose 2,6-bisphosphate content both in control and in thioacetamide-treated hepatocytes. However, phorbol 12-myristate 13-acetate stimulated 6-phosphofructo 2-kinase activity and increased fructose 2,6-bisphosphate concentration in thioacetamide-treated liver cells, whereas no similar response was found in hepatocytes from control rats. The response of postnecrotic thioacetamide-treated hepatocytes to phorbol 12-myristate 13-acetate was similar to that obtained from 22-day-old fetal liver cells, which reveals that different methods might control fructose 2,6-bisphosphate content and therefore the mechanisms of glycolysis and gluconeogenesis at this regulatory step. The lack of response to glucagon of glycogen phosphorylase a and 6-phosphofructo 2-kinase from thioacetamide-treated hepatocytes may indicate that the expression of specific enzymes of carbohydrate metabolism undergoes transitions to less-differentiated isoenzymatic forms. Moreover, the isoenzyme pattern of hexokinases elicits a complete disturbance in glucokinase and hexokinases activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Lack of control of liver gluconeogenesis in cholestatic rats with reduced portal blood flow.

Previous studies indicated a role for ischemia in the metabolic changes induced by cholestasis. Liver pyruvate kinase is a key enzyme for the concurrent control of glycolysis and gluconeogenesis. In this experiment the control of pyruvate kinase activity was investigated in cholestatic rats. Pyruvate kinase kinetics changed from a sigmoidal type in sham-operated rats to a hyperbolic type in obstructed rats. The change in the enzymatic kinetics paralleled the reduction in the portal blood flow, which reached 50% of the control value 7 days after obstruction. Dibutyryl cyclic AMP (5 mumol/kg body wt) plus theophylline 0.1 mmol/L failed to inactivate the enzyme when injected into the portal veins of rats whose livers were obstructed 7 days before. Both the kinetics changes and the lack of phosphorylation control are compatible with ischemia.

Animals↗
PubMed1992

The cooperative binding of fructose-1,6-bisphosphate to yeast pyruvate kinase.

The cooperative binding of the allosteric activator fructose-1,6-bisphosphate [Fru(1,6)P2] to yeast pyruvate kinase was investigated by equilibrium dialysis and fluorescence quench titration. The results show that yeast pyruvate kinase binds four molecules of Fru(1,6)P2 per tetramer and the observed fluorescence quench follows the binding of the ligand and not the cooperative T to R state transition. Additionally it is shown that the binding of Fru(1,6)P2 to yeast pyruvate kinase is compatible with the model of cooperativity that has been proposed and incorporates an intermediate state, R', with properties between those of the T and R states.

Allosteric Regulation↗
PubMed1992

pH dependence of the reverse reaction catalyzed by phosphofructokinase I from Escherichia coli: implications for the role of Asp 127.

The kinetics of the reverse reaction catalyzed by Escherichia coli phosphofructokinase, i.e., the synthesis of ATP and fructose-6-phosphate from ADP and fructose-1,6-bisphosphate, have been studied at different pH values, from pH 6 to pH 9.2. Hyperbolic saturations of the enzyme are observed for both substrates. The affinity for fructose-1,6-bisphosphate decreases with pH following the ionization of a group with a pK of 6.6, whereas the catalytic rate constant and perhaps the affinity for ADP are controlled by the ionization of a group with a pK of 6. Several arguments show that the pK of 6.6 is probably that of the carboxyl group of Asp 127, whereas the pK of 6 is tentatively attributed to the carboxyl group of Asp 103. The pK of 6.6 is assigned to the carboxyl group of Asp 127 in the free enzyme, and a simple model suggests that the same group would have an abnormally high pK, above 9.6, in the complex between phosphofructokinase and fructose-1,6-bisphosphate. It is proposed that the large pK shift of more than 3 pH units upon binding of fructose-1,6-bisphosphate is due to an electrostatic repulsion that could exist between the 1-phosphate group and the carboxyl group of Asp 127, which are close to each other in the crystal structure of phosphofructokinase (Shirakihara, Y. & Evans, P.R., 1988, J. Mol. Biol. 204, 973-994). The same interpretation would also explain the much higher affinity of the enzyme for fructose-1,6-bisphosphate when Asp 127 is protonated.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗
PubMed1992

Role of timing of administration in the cardioprotective effect of fructose-1,6-bisphosphate.

We administered fructose-1,6-bisphosphate (FDP), 1 mM, to isolated and perfused rabbit hearts submitted, after 90 minutes of equilibration, to an ischemic period (60 minutes at a coronary flow of 0.17 ml/min/g), followed by a period of reperfusion (30 minutes at a coronary flow of 3.6 ml/min/g). FDP was delivered at different times following the experimental protocol: 60 minutes before ischemia and for the entire experiment; 60 minutes before and during ischemia, but not at reperfusion; at the onset of ischemia and during reperfusion; and only during reperfusion. The FDP cardioprotective effect was evaluated in terms of recovery of left ventricular pressure developed during reperfusion, creatine phosphokinase (CPK) and noradrenaline release, mitochondrial function (expressed as yield, RCI, QO2, ADP/O), ATP and creatine phosphate (CP) tissue contents, calcium homeostasis, and by measuring oxidative stress in terms of reduced and oxidized glutathione release and tissue contents. Our data show that the cytoprotective action of FDP is closely related to the time of administration. Optimal myocardial preservation was achieved when it was present prior to ischemia and during reperfusion. When given at the time of ischemia or only on reperfusion, FDP does not exert cardioprotection. The data suggest that the FDP cardioprotective effect is related to improvement of energy metabolism.

Adenosine Triphosphate↗
PubMed1992

A kinetic description of sequential, reversible, Michaelis-Menten reactions: practical application of theory to metabolic pathways.

Equations are presented which describe a linear coupled system of reactions that utilize a single substrate and convert it to product by way of several intermediate enzyme catalysed steps. The present analysis extends previous results by assuming that the enzymes obey reversible Michaelis-Menten kinetics. In order for the system to reach steady state one must assume that the initial substrate concentration and the final product concentration are buffered to a constant value. Using the present analysis it can be shown that the system will not enter a steady state if the maximal velocity of any forward reaction is less than the steady state flux through the system. This condition represents a practical test for determining if a system will enter steady state but is valid only when the rate of the primary enzyme is not affected allosterically be intermediates in the pathway. The equations are used to analyse a portion of the rat liver glycogenic pathway that catalyses the conversion of glucose to fructose 1,6-bisphosphate.

Animals↗
PubMed1992

Oscillations in glycolysis: multifactorial quantitative analysis in muscle extract.

A multifactorial quantitative analysis of oscillations in glycolysis was conducted in the postmicrosomal supernatant of rat muscle homogenates incubated in the presence of yeast hexokinase. Oscillations in adenine nucleotides, D-fructose 1,6-bisphosphate, triose phosphates, L-glycerol 3-phosphate, 3HOH generation from D-[5-3H]glucose, NADH and L-lactate production were documented. The occurrence of such oscillations were found to depend mainly on the balance between the consumption of ATP associated with the phosphorylation of D-glucose, as catalyzed by both yeast and muscle hexokinase, and the net production of ATP resulting from the further catabolism of D-fructose 6-phosphate, as initiated by activation of phosphofructokinase. The oscillatory pattern was suppressed in the presence of D-fructose 2,6-bisphosphate. It is proposed that the quantitative information gathered in this study may set the scene for further studies in extracts of cells other than myocytes, e.g. hepatocytes and pancreatic islet cells, in which no oscillation of glycolysis was so far observed.

Adenine Nucleotides↗
PubMed1977

Fructose-1,6-bisphosphate, a regulator of metabolism.

Fructose-1,6-bisphosphate affects the rate of a large variety of enzyme reactions. In some instances its role as a physiologic effector is well documented. In many cases the effects of fructose bishosphate on particular enzymes have been demonstrated in vitro but the link to physiologic conditions has not yet been established. It is the purpose of this paper to summarize the scattered findings in fructose bisphosphate as an effector of enzyme reactions and to draw some conclusions about the role of the compound in metabolic regulation.

Carbohydrate Metabolism↗
PubMed1979

Differential function of the phosphoglucomutase isozymes PGM1 and PGM2.

A total of 13 metabolites thought to be possibly inhibitory were tested for their influence on PGM isozyme activities, each at several different concentrations. The analysis of statistical significance was based on enzyme activities obtained by densitometric measurements of starch gels. Five of the substances were found to inhibit PGM activity, three of which definitely and a further one probably led to a significantly stronger inhibition of the isozymes of the PGM2 locus than of PGM1 isozymes. They are (1) fructose-1,6-diphosphate, (2) adenosine triphosphate, (3) citrate, and (4) possibly 2,3-diphosphoglycerate. Thus, PGM1 isozymes proved to function better in hard or perhaps marginal metabolic conditions. Related evolutionary aspects are discussed.

Adenosine Triphosphate↗