Zinc as Activating Cation for Muscle Glycolysis

Abstract

Zinc cation performed a role of activator as well as inhibitor for production of lactate from glucose 6-phosphate in the cytosol fraction of rat muscle. The pH optimum for glycolysis was 7.3 when Zn²⁺ acted as an activator. At concentrations lower than 0.46mM, Zn²⁺ was shown to be a more effective activator than Mg²⁺ with an apparent K_1/2 of approximately 0.1mM. However, at concentrations higher than 0.5mM, Zn²⁺ inhibited lactate production. The activatory as well as inhibitory effect of Zn²⁺ on lactate production was investigated by the estimation of glycolytic intermediates. From the crossover plot, lactate production reflected phosphofructokinase activity, when Zn²⁺ was used as a catalytic cation for both reactions. Phosphofructokinase activity in purified muscle was activated by Zn²⁺ with an apparent K_m of approximately 0.05mM, but at high Zn²⁺ concentrations, the enzyme activity was inhibited with an I₅₀ of 0.23mM in the presence of ATP. From these findings, it appears that lactate production might also depend on phosphofructokinase activity when Zn²⁺ is used as an activating cation.