Abstract
The activity of chicken liver mevalonate 5-diphosphate decarboxylase was measured over a wide range of Mg 2+ and ATP concentrations. It was found that free ATP activated the enzyme, whereas free Mg 2+ had no effect on the enzyme activity. Computed analyses of free species concentrations and pH studies indicated that MgATP 2- is the true substrate. The relative efficiencies of Mg 2+, Mn 2+, Cd 2+, and Zn 2+ as activating metal ions were evaluated in terms of V/ K m for the corresponding (metal-ATP) 2- complexes, and the relative ratios were: Mn 2+ 100, Cd 2+ 37, Mg 2+ 14, Zn 2+ 1.7. Inhibitory effects were demonstrated for all free divalent cations tested, except for Mg 2+, and were in the order Zn 2+ > Cd 2+ > Mn 2+.
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