Abstract
The pyruvate kinase (ATP:pyruvate phosphotransferase, EC 2.7.1.40) isoenzymes from kidney cortex have been studied further. Pyruvate kinase type I which is the major component, shows homotropic cooperativity towards the substrate phosphoenol pyruvate, the effect is independent of pH. This isoenzyme is markedly inhibited by alanine and other amino acids but its activity is not modified by ATP or fructose 1,6-diphosphate. The kinetic behavior of this isoenzyme is then clearly different from that of the other pyruvate kinases from rat tissues. Pyruvate kinase type II exhibits sigmoid kinetics with respect to phosphoenolpyruvate. The enzyme is activated by fructose 1,6-diphosphate and inhibited by ATP, alanine and cysteine. The allosteric properties of the enzyme are strongly affected by changes in the pH. It is concluded that this kidney cortex isoenzyme is very similar to the pyruvate kinase type L from liver.
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