The activity and kinetic properties of mevalonate kinase in superovulated rat ovary

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 K(m) of a partially purified preparation of mevalonate kinase for dl-Mevalonate was 3.6+/-0.5mum; its K(m) for MgATP(2-) was 120+/-7.7mum. 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 MgATP(2-). The K(i) for inhibition by geranyl pyrophosphate was 1.3+/-0.2mum; the K(i) for inhibition by farnesyl pyrophosphate was 1.0+/-0.3mum. These findings are discussed with reference to the control by luteinizing hormone of steroidogenesis from acetate.