Purification and characterization of avian liver mevalonate-5-pyrophosphate decarboxylase

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Abstract
Mevalonate-5-pyrophosphate decarboxylase was purified 5800 times from chicken liver and obtained in a stable and highly purified form. The protein is a dimer of MW 85,400 .+-. 1941, and its subunits were not resolved by gel electrophoresis in denaturing conditions. The purified enzyme does not require the presence of SH-containing reagents for either activity or stability. The enzyme shows a high specificity for ATP and requires for activity a divalent metal cation, Mg2+ being most effective. The optimum pH for the enzyme ranges from 4.0-6.5. Inhibitory effects for the enzyme activity were detected by citrate, phthalate, and phosphate. The isoelectric point, as determined by column choromatofocusing, is 4.8. The kinetics are hyperbolic for both substrates, showing a sequential mechanism; true Km values of 0.0141 mM and 0.504 mM were obtained for mevalonate-5-pyrophosphate and ATP, respectively.