Effect of different allylic diphosphates on the initiation of new rubber molecules and on cis-1,4-polyisoprene biosynthesis in guayule (Parthenium argentatum Gray)

Natural rubber biosynthesis is the rubber-particle-bound rubber-transferase-catalyzed cis-1,4-polymerization of isoprene monomers derived from isopentenyl diphosphate (IPP). In addition to IPP, allylic diphosphate is required to initiate new rubber molecules. In this paper we describe, for the first time, detailed kinetic analyses of rubber molecule initiation and polymerization in Parthenium argentatum Gray. We compare the effects of four different allylic diphosphate initiators on the rate of rubber biosynthesis using [C-14]IPP. Also, we compare the rates of rubber molecule initiation and polymerization using [H-3]allylic diphosphates as well as [C-14]IPP. Under non-limiting substrate concentrations, new rubber molecules were initiated and terminated at a constant rate for each initiator. The rate of rubber biosynthesis increased with the chain length of the initiator up to C-15. Our results indicate that initiation regulates the overall rate of rubber biosynthesis. Therefore, strategies to enhance in vivo rubber yield by genetic manipulation should focus on rubber molecule initiation.