Control of pyruvate kinase activity in the lens

Abstract

Lens pyruvate kinase (PK) was found to be a variant of the M 2 PK isozyme. It was inhibited by ATP and a number of l-amino acids; Mg 2+ abolished the ATP effect, whereas l-serine counteracted the amino acid inhibition. Pre-incubation of lens PK with fructose-1,6-diphosphate promoted the enzyme affinity toward phosphoenolpyruvate. This property was preserved in human senile cataractous lenses. A decrease of PK specific activity was noted in the epithelium of some cataractous lenses, but the residual activity was at least 15 times that of phosphofructokinase. The activity of PK was apparently determined by the catalytic activity of phosphofructokinase, and also by the cellular concentrations of ATP and amino acids such as alanine.