Kinetic analysis of enzyme reactions. II. The potassium activation and calcium inhibition of pyruvic phosphoferase.

Muscle pyruvic phosphoferase,l catalyzing the reaction PEPA + ADP a pyruvate + ATP,2 has been shown to require both Mg+ (3) and K+ or NHb+ ions (4-6) for maximum activity and to be strongly inhibited by Ca+f (4, 5). The mechanism of action of these ions is not known. The principal objective of the research reported in this paper was to acquire information about the activation by K+ ions through the application of kinetic studies. Recent extensions of the theory of enzyme inhibition and activation (7) serve as a basis for the experimental approach applied in this paper. A second objective of this research was to determine whether the activation of rabbit muscle pyruvic phosphoferase was essential or only stimulatory. In previous work (4, 5) the possible indispensable requirement of K+ for rat muscle pyruvic phosphoferase was left open to question.