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 [3H]isopentenyl pyrophosphate were studied. The Km values for farnesyl pyrophosphate and isopentenyl pyrophosphate were found to be 25 microM and 4.4 microM, 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.