CHARACTERIZATION AND DISTRIBUTION OF CIS-PRENYL TRANSFERASE PARTICIPATING IN LIVER MICROSOMAL POLYISOPRENOID BIOSYNTHESIS

The properties of rat liver cis-prenyl transferase, mediating the synthesis of polyisoprenoid pyrophosphate from trans,trans-farnesyl pyrophosphate and [H-3]isopentenyl pyrophosphate were studied. The K(m) values for farnesyl pyrophosphate and isopentenyl pyrophosphate were found to be 25-mu-M and 4.4-mu-M, respectively. Appropriate conditions were established to measure the condensation reaction, which was linear during the first hour using 1 mg microsomal protein. Various detergents could solubilize the enzyme, but the presence of Triton X-100 was required during the incubation to obtain full activity. There was also an absolute requirement for Mg2+ and the pH maximum was 7.0. Inorganic phosphate, especially pyrophosphate, proved to be inhibitory. cis-Prenyl transferase is associated mainly with the cytoplasmic surface of rough microsomes and, to some extent, also with smooth I microsomes, but was almost absent from smooth II microsomes. At all localizations, the product is polyprenyl pyrophosphate and to some extent, also polyprenyl monophosphate. The isoprenoids formed contain 15-18 units in the presence of detergents and 16-20 units in the absence of detergents.