[Characterization of free and bound pyruvate kinase in the brain of the teleost fish mullet].

Activity of pyruvate kinase free and bound with the structural components that has been revealed in brain of red mullet. The bound form disappeared as a result of 1.5 hour hypoxia. The Hill coefficients for phosphoenolpyruvate and ADP of the both enzyme forms were about 1, but the Michaelis constants of free enzyme for the phosphoenolpyruvate and ADP were 2-3 times higher than that for the bound form. The pH-dependence of the both enzymes was similar. The free enzyme was studied as a result of heating probes at 45 degrees C during 15 minutes, but the bound form was successively activated and stabilized within this procedure. The ATP inhibition of the both forms was the same. Fructose-1,6-bisphosphate and alanine does not affect the pyruvate kinase activity. Possible mechanisms for regulation of kinetic properties and redistribution of pyruvate kinase between free and bound states are discussed.