Zinc as activating cation for muscle glycolysis

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 0.46 mM, Zn2+ was shown to be a more effective activator than Mg2+ with an apparent K 1/2 of approximately 0.1 mM. However, at concentrations higher than 0.5 mM, 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 Km of approximately 0.05 mM, but at high Zn2+ concentrations, the enzyme activity was inhibited with an I50 of 0.23 mM 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.