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At least 973 records · Page 54Linked to original sources
PubMed1980

Unchanged glycolytic capacity in rat kidney under conditions of stimulated gluconeogenesis. Determination of phosphofructokinase and pyruvate kinase in microdissected nephron segments of fasted and acidotic animals.

The glycolytic capacity in rat kidney was studied under conditions of stimulated gluconeogenesis like 48 h starvation and 48 h acidosis induced by force-feeding with a NH4Cl/glucose solution. Rats fed ad libitum and force-fed with a glucose solution served as controls. The specific activities of the key enzymes phosphofructokinase and pyruvate kinase were determined in single segments of the nephron. The determinations were performed by microdissection of lyophilized tissue sections followed by enzymatic analysis, including oil well technique, enzymatic amplification, and fluorometric measurement. In the distal portion of the nephron of both fed and force-fed animals a 10-fold higher specific activity of phosphofructokinase and pyruvate kinase was found compared with the proximal portion, known as the site of renal gluconeogenesis. Starvation and acidosis altered neither the distribution pattern nor the specific activities of these enzymes. From these results it is concluded that renal glycolysis does not undergo alterations at the level of enzymatic activities in favour of renal gluconeogenesis, probably because of the separate localization of both pathways within the nephron.

Acidosis↗
PubMed1985

[Pyruvate kinase deficiency in the newborn infant].

4 cases with haemolytic anemia associated with pyruvate kinase deficiency from 3 different families are presented. Different clinical development during the first year of life is demonstrated and discussed.

Anemia, Hemolytic↗
PubMed1975

Acquired red cell pyruvate kinase deficiency in leukemias and related disorders.

The authors studied red blood cell pyruvate kinase activity of 202 patients with various hemopathies. A PK deficiency of moderate grade was found in 39% of patients with acute myeloblastic leukemias, in 57% of those with primary medullary insufficiency without aplasia, in 61% of those with refractory sideroblastic anemia. The PK deficiency was often associated with deficiencies of other red cell enzymes. The mechanism of such enzyme abnormalities was discussed with the hypothesis of a post-translational molecular alteration.

Anemia↗
PubMed1981

[Interrelationship between two kinetic forms of pyruvate kinase in chicken liver during ontogenesis].

The value of the r coefficient for pyruvate kinase (rate at 1.5 mM of phosphoenolpyruvate per rate at 0.4 mM of phosphoenolpyruvate), i.e. ratio between the enzyme forms possessing the Michaelis-Menten and cooperative kinetics, in chicken liver during ontogenesis was found to be different. The embryonic liver contains predominantly the form with the cooperative kinetics, while in the livers of 1- and 10-day-old chickens the content of the other form is increased. In the livers of adult chicken the correlation between the two forms is that typical for 10-day-old chicken.

Aging↗
PubMed1986

Synergistic effect of ammonium and potassium ions on pyruvate kinase from Ehrlich ascites tumor cells.

The effect of NH4+ on M2-pyruvate kinase isolated from Ehrlich ascites tumor cells was investigated. The enzyme is activated by NH4+ more efficiently than by K+. Moreover, a synergistic interaction of the two cations is observed since NH4+ increases the affinity of the enzyme for K+. The affinity of the enzyme for phosphoenolpyruvate is also increased in the presence of NH4+, and in these conditions the activating effect of fructose-1,6-bisphosphate is reduced. It is proposed that NH4+ be considered a specific allosteric activator of the tumor enzyme.

Ammonia↗
PubMedDate not supplied

[Pyruvate kinase isoenzymes in the kidneys of rabbits with insular insufficiency].

Two isoenzymes of pyruvate kinase--PK-1 and PK-2 were obtained from the cortical layer of rabbit kidney by the method of chromatography on DEAE-cellulose. Starvation of rabbits for 10--16 days and alloxan diabetes produced no significant changes in the specific activity of PK in the soluble fraction obtained from the cortical layer of rabbit kidney. However, there were significant shifts in the isoenzymatic spectrum of the PK of the kidneys in rabbits with alloxan diabetes: the activity of the PK-1 increased considerably and significantly, and the isoenzyme PK-2 disappeared almost completely.

Animals↗
PubMed1988

Two homozygous cases of erythrocyte pyruvate kinase (PK) deficiency in Japan: PK Sendai and PK Shinshu.

Two new erythrocyte pyruvate kinase (PK) variants with severe nonspherocytic hemolytic anemia are presented. These cases are both considered to be homozygous because of the consanguineous marriages in their parents. Their erythrocyte PK's were characterized by the recommended methods of the International Committee for Standardization in Haematology (ICSH). These two variants have been named PK Sendai and PK Shinshu. PK Sendai showed a high K0.5S (phosphoenolpyruvate), was remarkably inhibited by ATP, and was thermolabile, while PK Shinshu demonstrated remarkably low enzyme activity and required a high level of fructose 1,6-diphosphate for activation.

Adolescent↗
PubMed1983

Effect of fructose 1,6-bisphosphate on the activity of liver pyruvate kinase after limited proteolysis with cathepsin B.

Treatment of rat liver-type pyruvate kinase with rabbit liver cathepsin B at pH 7.0 caused loss of activity in the standard assay with 0.6 mM of phosphoenolpyruvate. The modified enzyme exhibited about 10% of the original activity when assayed with 2.0 mM of the substrate. No detectable change in the subunit molecular weight of the enzyme occurred during inactivation. On addition of 4 microM fructose 1,6-bisphosphate the activity of the treated enzyme was restored to that of the original enzyme. Limited proteolysis of the enzyme by cathepsin B appears to enhance the requirement for the positive effector, fructose 1,6-bisphosphate.

Animals↗
PubMed1994

An autopsy case of pyruvate kinase deficiency anemia associated with severe hemochromatosis.

We report an autopsy case of pyruvate kinase deficiency anemia with severe hemochromatosis. This anemia is rarely associated with hemochromatosis. In this case, the autopsy findings showed hemochromatosis of the heart, pancreas, liver, kidneys, thyroid gland, adrenal glands, testes and skin. Microscopic examination showed iron depositions in these organs, but not in the bone marrow. A family study showed negative data for iron overload and no known HLA type suggestive of idiopathic hemochromatosis. To explain this rare association, we suggest that this patient's iron overload was an acquired type, which might have mainly been caused by increased iron absorption due to the severe hemolytic anemia.

Adult↗
PubMed1980

Seven pyruvate kinase variants characterized by the ICSH recommended methods.

Seven new red-cell pyruvate kinase (PK) variants were characterized by the methods recently recommended by the International Committee for Stanardization in Haematology. The cases were all true homozygote as evidenced by consanguineous marriages of the parents; all are Japanese. These variants were designated as PK Tokyo, PK Nagasaki, PK Sapporo, PK Maebashi, PK Itabashi, PK Fukushima and PK Aizu, respectively. Low substrate affinity (high K0.5S for phosphoenolpyruvate) and thermal instability appear to play major roles in causing defective enzyme function, resulting in chronic haemolytic anaemia. Product inhibition of PK by ATP may also play an additional role in causing haemolysis in more than half the cases.

Adolescent↗
PubMed1975

Effects of calcium ions on pyruvate kinase from human erythrocytes.

Ca2+ ions have a biphasic effect on the allosteric pyruvate kinase (EC 2.7.1.40) from human erythrocytes: Ca2+ is an activator at low phosphoenolpyruvate (PEP) concentrations: at increased PEP concentrations Ca2+ behaves as an inhibitor. In the presence of ATP the same effect was observed and at low PEP concentrations Ca2+ ions can completely abolish the ATP inhibitory effect. At high Ca2+ concentrations there is a loss of the cooperativity towards PEP. The enzyme activated by fructose-1,6-diphosphate (FDP) is inhibited by Ca2+ ions at all concentrations of PEP tested. Mg2+ ions are not able to counteract the activation by Ca2+ ions at low PEP concentrations. The results are interpreted on the basis of the model of Monod.

Adenosine Triphosphate↗
PubMed1984

Hemin-induced conversion of pyruvate kinase isozymes in K562 cells.

The effects of hemin on the conversion of pyruvate kinase (PK) isozymes from the M2-type to the L-type in K562 cells were investigated. Immunofluorescence, ion exchange chromatography, and electrophoretic studies showed that the untreated K562 cells contained only the M2-type PK, while eight to 20 days after induction with hemin, concomitant with hemoglobin F synthesis, L-type PK levels increased while M2-type PK levels decreased. Electrophoretic study revealed three hybrid isozymes of the L-type and M2-type PK. We conclude that the conversion of PK isozymes from the M2-type to the L-type in erythroid precursor cells occurs in the early stage of maturation.

Cell Line↗
PubMed1980

Analysis of progress curves. Rate law of pyruvate kinase type I from Escherichia coli.

Progress curves of the reaction catalysed by pyruvate kinase from Escherichia coli K12, designed to cover the four-dimensional concentration space of phosphoenolpyruvate, ADP, Mg2+ and ATP in the regulatory region, were recorded with the pH-stat method (pH 7.0 and 25 degrees C). Additional initial-rate measurement were performed to assess specific points. Two methods for the evaluation of progress curves were used: fitting the rate law to the rates obtained from the tangents of the progress curves and fitting the integrated rate law directly to the curves. Two models, both extensions of the concerted model given by Monod, Wyman & Changeux [(1965) J. Mol. Biol. 12, 88--118] with four protomers, could be fitted to the data within the experimental error. Model discrimination in favour of one of these models was possible by proper experimental design. In the selected model one conformational state of the enzyme forms the active complex. The active site of a second conformational state forms abortive complexes with Mg2+, causing strong inhibition at high Mg2+ concentrations. In the absence of ligands, most of the enzyme is in a third state that binds ATP at an allosteric site.

Adenosine Diphosphate↗
PubMed1982

Immunocytochemical study of pyruvate kinase isoenzymes in normal and pathologic human liver.

In healthy human livers, L pyruvate kinase (L PK) was detected by immunofluorescence and double labelling in hepatocytes and M PK was detected in bile duct epithelial cells. Numerous associations between isoenzyme type and hepatological lesion were observed. In 10 cases of ethanolic cirrhosis, L and M PK were simultaneously observed in the hepatocytes of regenerative nodules, as they were in biliary neoductules; fibrotic regions were L and M PK negative and the hepatocytes in the anastomosing plate system were almost exclusively L PK positive, as in normal subjects. In 12 hepatocarcinomas, cancer cells had a double L and M specificity with variations in the intensity of the M isoenzyme, while the stroma reaction was L and M negative. In five hepatoblastomas, the simultaneous presence of L and M PK was also observed, but the consistently marked intensity of M PK argues in favour of the embryonic nature of this type of cancer. The results suggest that mature, highly differentiated cells exclusively and specifically synthesize one isoenzyme. A double specificity in pathology reflects the dysfunctional state of the hepatic and biliary epithelial cells or a dedifferentiated state which may terminate with the appearance of a cancer.

Adult↗
PubMed1991

Characterization of pyruvate kinase of Trypanosoma brucei and its role in the regulation of carbohydrate metabolism.

Pyruvate kinase from Trypanosoma brucei is a labile enzyme, losing its activity within several hours. In mixtures containing 50 mM triethanolamine buffer, pH 7.2, 25% glycerol and 0.5 mM inorganic phosphate the enzyme remained active and could be purified to homogeneity with a specific activity of 417 units mg-1 and a yield of 65%. The enzyme has an activation energy of 31.9 kJ mol-1. Magnesium and potassium ions are essential for activity. Cobalt or manganese ions replace Mg2+ but this leads to a decrease in maximal velocity. Potassium ions can be substituted by ammonium ions, while sodium ions behave as a competitive inhibitor with respect to both K+ and NH4+. All metal ions studied displayed sigmoidal kinetics. The enzyme is activated, with decreasing efficiency by fructose 2-phosphorothioate 6-phosphate, fructose 2,6-bisphosphate, fructose 1,6-bisphosphate and glucose 1,6-bisphosphate. They all display hyperbolic kinetics. Glycerate 2,3-bisphosphate, glyceraldehyde 3-phosphate, CoASAc, oxalate, AMP, ADP, and ATP inhibit the enzyme. At substrate saturation PK was activated by Pi up to a concentration of 0.8 mM. At higher Pi concentrations the enzyme is inhibited. The enzyme is unaffected by most amino acids, only phenylalanine stimulates and tyrosine inhibits.

Amino Acids↗