Methods are described for the assay and partial purification of mevalonate kinase from superovulated rat ovary. The total activity of mevalonate kinase in superovulated rat ovary was 1.6±0.14units/g wet wt.; it was unchanged by the administration of luteinizing hormone in vivo. The Km of a partially purified preparation of mevalonate kinase for dl-Mevalonate was 3.6±0.5μm; its Km for MgATP2− was 120±7.7μm. The enzyme was inhibited by geranyl pyrophosphate and farnesyl pyrophosphate, but not by isopentenyl pyrophosphate or 3,3′-dimethylallyl pyrophosphate. dl-mevalonate 5-phosphate inhibited at high concentrations. With both geranyl pyrophosphate and farnesyl pyrophosphate the inhibition was competitive with respect to MgATP2−. The Ki for inhibition by geranyl pyrophosphate was 1.3±0.2μm; the Ki for inhibition by farnesyl pyrophosphate was 1.0±0.3μm. These findings are discussed with reference to the control by luteinizing hormone of steroidogenesis from acetate.
