INHIBITORY EFFECTS OF Zn2+ ON MUSCLE GLYCOLYSIS AND THEIR REVERSAL BY HISTIDINE

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Of a number of divalent cations investigated, Zn2+ strongly inhibited lactate production from glucose 6-phosphate in rat muscle cytosol fraction. The I50 value for lactate production influenced by Zn2+ was 10μM and was increased to 200μM and 18μM by the addition of 10mM histidine and 10mM carnosine, respectively. The inhibitory effect of 50μM Zn2+ on lactate production was completely reversed by the addition of 1.2mM histidine and the apparent Km was found to be 0.34mM. The inhibitory site for Zn2+ was investigated by the estimation of glycolytic intermediates. It occurred at point between fructose 6phosphate and fructose 1, 6-bisphosphate. Purified rat muscle phosphofructokinase was inhibited by Zn2+. The I50 values for Zn2+ were calculated to be 12, 5.5 and 1.5μM in the presence of 3, 0.3 and 0.06mM fructose 6-phosphate, respectively. The addition of histidine removed the inhibitory effect of Zn2+ on the glycolytic key enzyme. These studies indicate that in rat skeletal muscle the inhibitory effect of Zn2+ on lactate production might result from the inhibition of phosphofructokinase and that histidine could remove the effect.
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