SUMMARY

The specific activity of Coprinus lagopus pyruvate kinase is high under con-ditions of glycolysis but low under conditions of gluconeogenesis. Only a single form of the enzyme was detectable, the properties of which resemble in a number of respects those of the allosteric forms of pyruvate kinase. These properties include co-operative interactions with phosphoenolpyruvate (PEP), ATP and fruc-tose I,6-diphospate. Fructose I,6-diphosphate (FDP) almost completely reverses the inhibitory effects of ATP. The decrease in substrate co-operativity in the presence of FDP, the allosteric activator and the increase in ATP co-operativity in the presence of activator suggests the enzyme can be classed as a ‘K-system ’ allosteric protein. The regula-tory properties of Coprinus Zagopus pyruvate kinase (ATP-pyruvate phospho-transferase, EC 2.7. I.40) are discussed in relation to differences in allosteric pyruvate kinases from other sources