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PubMed1976

Biphasic reaction kinetics in an anomalous isozyme of erythrocyte pyruvate kinase.

A mutant erythrocyte isozyme of pyruvate kinase (PK) (ATP: pyruvate phosphotransferase, EC 2.7.1.40) has been found in associatin with chronic hemolytic anemia in two siblings who were doubly heterozygous for the isozyme and for quantitative PK deficiency of the usual form. The isozyme was characterized by approximately normal maximum reaction velocities but had markedly decreased affinity for the substrate, phosphoenolpyruvate (PEP), with 5-fold to 10-fold increases in half-saturation constants and decreased interaction between substrate binding sites. Two distinctly separable kinetic patterns for PEP were observed with multiple specimens. Concentrations of fructose 1,6-diphosphate (FDP) required for half-maximal activation were two orders of magnitude greater than controls, and optimal pH was lowered to 6.5. stability at 4 degrees C was markedly decreased, but the lost enzyme could be reactivated by fdp for periods even longer than normal controls.

Adenosine Diphosphate↗
PubMed1984

Dietary control of aldolase B and L-type pyruvate kinase mRNAs in rat. Study of translational activity and hybridization with cloned cDNA probes.

Liver L-type pyruvate kinase and aldolase B mRNAs are the two species whose translational activity increases the most after feeding starved rats a high carbohydrate diet (Simon, M. P., Besmond, C., Cottreau, D., Weber, A., Chaumet-Riffaud, P., Dreyfus, J. C., Sala Trépat, J., Marie, J., and Kahn, A. (1984) J. Biol. Chem., in press). We therefore compared the pattern of this induction in three tissues synthesizing these enzymes, e.g. the liver, small intestine, and kidney. Influence of high lipid and protein diets on liver L-type pyruvate kinase and aldolase B mRNAs was also investigated. In the starved rat livers, L-type pyruvate kinase mRNA was practically undetectable. Carbohydrate diet induced an increase of both mRNA concentrations, with a maximum at the 12-18th h; at this time, mRNA concentration was increased about 4-8 times for aldolase B and 40-100 times for L-type pyruvate kinase, translational activities representing about 1% of the total mRNA activity for both enzymes. After the 24th h of carbohydrate diet, mRNA concentrations decreased slightly, then remained in plateau. In animals refed the high carbohydrate diet, starvation as well as high lipid and protein diets provoked a rapid decrease of both mRNA concentrations and translational activities. In the kidney, aldolase B mRNA synthesis was high in starved rats and was only slightly stimulated by carbohydrates (1.5-2.5 times). L-type pyruvate kinase mRNA concentration was increased 6-15-fold after feeding a high carbohydrate diet. In the small intestine, in contrast, the extent of aldolase B mRNA induction by a carbohydrate diet was similar to that in the liver, while L-type pyruvate kinase mRNA concentration was practically similar in starved and refed rats (about 1:10 of the concentration observed in refed rat liver). These results seem to indicate that the mechanisms responsible for carbohydrate induction of L-type pyruvate kinase and aldolase B are different. In addition, dietary control of each enzyme is also different in the various tissues which synthesize them.

Animals↗