BIOSYNTHESIS OF PRENYL DIPHOSPHATES BY CELL-FREE-EXTRACTS FROM MAMMALIAN-TISSUES

When assayed by the conventional method for prenyltransferase using a combination of [1-C-14] isopentenyl and geranyl diphosphates, 100,000 x g supernatants of homogenates of rat liver and brain catalyzed the f ormation of geranylgeranyl diphosphate at a much lower rate than that of farnesyl diphosphate. Surprisingly, however, the formation of geran ylgeranyl diphosphate in incubations of [1-C-14]isopentenyl diphosphat e alone with these enzyme systems was comparable to that of farnesyl d iphosphate. Addition of dimethylallyl diphosphate to the same enzyme s ystems in the presence of [1-C-14] isopentenyl diphosphate resulted in a marked increase in the rate of formation of farnesyl diphosphate, w hile the rate of formation of geranylgeranyl diphosphate was saturated . Metabolic labeling of rat liver and kidney slices with [5-H-3]mevalo nic acid revealed that the major prenyl residue of the detectable pren ylated proteins was actually the geranylgeranyl group. Coupled with th e previous finding that geranylgeranyl diphosphate accumulates during metabolic labeling of rat liver slices with [2-H-3] mevalonic acid [Sa gami, H., Matsuoka, S., and Ogura, K. (1991) J. Biol. Chem. 266, 3458- 3463], these results indicate that the rate of de novo synthesis of ge ranylgeranyl diphosphate from mevalonic acid is comparable to that of farnesyl diphosphate.