The enzymatic incorporation of isopentenyl pyrophosphate into polyisoprene in rubber particles from Parthenium argentatum Gray

Studies have indicated the presence of both a de novo biosynthesis of new polyisoprene chains and the elongation of pre-existing rubber-PP chains in rubber particles from Ficus elastica Roxb. and small rubber particles from Hevea brasiliensis (Willd. ex A. Juss.) Müll. Arg. In this paper, we have isolated rubber particles from the cortical parenchyma of Parthenium argentatum Gray with an adsorbed isopentenyl pyrophosphate isomerase that was competent to form polyisoprene to determine the presence of de novo biosynthesis of polyisoprene and the elongation of pre-existing rubber-PP. The gel filtrated rubber particles were supplied saturating concentrations of [¹⁴C]-isopentenyl pyrophosphate for 1 h and the resulting concentrations of [¹⁴C]-polyisoprene were isolated and analyzed with a Waters 150C Gel Permeation Chromatograph. The mol wt distribution of the [¹⁴C]-polyisoprene ranged from 10³ to 10⁶ Da with no formation of high mol wt chains equal to the polyisoprene in the mol wt distribution of natural rubber from P. argentatum. The mol wt distribution of [¹⁴C]-polyisoprene following 1 h of incubation of the reaction mixture was similar to the mol wt distribution formed by the bound rubber transferase in washed rubber particles of H. brasiliensis and the time-dependent formation of polyisoprene by washed rubber particles from P. argentatum. The data support the conclusion that the washed rubber particles from P. argentatum contain a bound rubber transferase that initiates the formation of new chains of polyisoprene from the dimethylallyl pyrophosphate initiator generated from the added isopentenyl pyrophosphate isomerase followed by the extensive polymerization of isopentenyl pyrophosphate to form a monomodal rubber polymer. There was no evidence in these washed rubber particles of a chain elongation of pre-existing rubber-PP.