THE SEPARATE ROLES OF PLANT CIS AND TRANS PRENYL TRANSFERASES IN CIS-1,4-POLYISOPRENE BIOSYNTHESIS

In plants, the elongation of cis-1,4-polyisoprene (natural rubber, M(r) > 10(6)) requires a small trans-allylic diphosphate (less-than-or-equal-to C20) initiator. The trans-allylic diphosphates are hydrophilic cytosolic compounds, whereas cis-1,4-polyisoprene is hydrophobic and compartmentalised in subcellular rubber particles. In this paper, it is demonstrated that soluble trans-prenyl transferase from latex of Hevea brasiliensis functions solely as farnesyl diphosphate synthase, and plays no direct role in cis-1,4-polyisoprene elongation. The cis-1,4-prenyl transferase is firmly associated with the H. brasiliensis rubber particle, as is also the case in other rubber-producing species [Archer, B. L., Audley, B. G., Cockbain, E. G. & McSweeney, G. P. (1963) Biochem. J. 89, 565-574; Madhavan, S., Greenblatt, G. A., Foster, M. A. & Benedict, C. R. (1989) Plant Physiol. 89,506-511; Siler, D. J. & Cornish, K. (1993) Phytochemistry 32, 1097-1102]. The experimental data explain and refute previous reports in which soluble trans-prenyl transferase isolated from H. brasiliensis latex was attributed both trans-prenyl transferase and cis-prenyl transferase activities [Light, D. R. & Dennis, M. S. (1989) J. Biol. Chem. 264,18589-18597; Light, D. R., Lazarus, R. A. & Dennis, M. S. (1989) J. Biol. Chem. 264,18598-18607]. Thus, it appears that plant prenyl transferases are comparable to animal enzyme systems in which trans-prenyl transferases are soluble enzymes whilst cis-prenyl transferases are membrane-bound [Ericcson, J., Runquist, M., Thelin, A., Andersson, M., Chojnacki, T. & Dallner, G. (1992) J. Biol Chem. 268,832-838].