CHARACTERIZATION OF 2 DISTINCT ALLYL PYROPHOSPHATASE ACTIVITIES FROM RAT-LIVER MICROSOMES

We have identified and characterized two novel allyl pyrophosphatase a ctivities from rat liver microsomes. One specifically hydrolyzes farne syl pyrophosphate (FPP) to farnesol and the other converts geranylgera nyl pyrophosphate (GGPP) to geranylgeranol. Hence, we named them farne syl pyrophosphatase (FPPase) and geranylgeranyl pyrophosphatase (GGPPa se) activities, respectively. Other allyl pyrophosphates, i.e., isopen tenyl pyrophosphate, dimethyl allyl pyrophosphate, and geranyl pyropho sphate, did not act as substrates for these activities. Both activitie s are metal ion independent and exhibit acidic pH optima (5.5 and 6.0) . Microsomal FPPase has a K-m for FPP of 7 mu M and a specific activit y of 6.8 nmol/min/mg protein at pH 5.5. GGPP is a potent noncompetitiv e inhibitor of FPPase. FPP has no inhibitory effect on GGPPase activit y. Microsomal GGPPase has a K-m for GGPP of 12 mu M and a specific act ivity of 14 nmol/min/mg protein. The K-m of FPPase activity for FPP in creases with an increase in pH. The GGPPase activity remains unaffecte d with an increase in pH. Metal ions Zn2+ and Mn2+ are potent inhibito rs of GGPPase activity. Zaragozic acid B is a weak inhibitor of FPPase /GGPPase activities as compared to squalene synthase. GGPPase activity is inhibited with a fourfold higher IC50 (20 mu M) as compared to FPP ase (5 mu M). Hence, the FPPase and GGPPase activities can be differen tiated by zaragozic acid B inhibition. Kinetic analysis of inhibition of FPPase by zaragozic acid B further indicates that it is a mixed typ e noncompetitive inhibitor. (C) 1994 Academic Press, Inc.