Structure of in vitro synthesized rubber from fresh bottom fraction of Hevea latex

Abstract

Bottom fraction (BF) separated from fresh Hevea brasiliensis latex by ultracentrifugation, after preincubation at 4° overnight, produced new rubber on incubation at 37° for 6 hr. The rubber yield was increased about 3.2- and 4.7-fold by the addition of isopentenyl diphosphate (IDP) and farnesyl diphosphate (FDP), respectively. The rubber formed on incubation in the presence of FDP showed a clearly bimodal molecular-weight distribution (MWD) with M n of 9.6 × 10 4 and M w of 1.0 × 10 6; which were about 1 4 of that of the endogenous rubber. This indicates that the formation of new rubber in BF uses FDP as a direct initiator. The presence of the dimethylallyl-group of the initiating species was observed in the new rubber formed on incubation of fresh BF with FDP, although it was not detected in in vivo rubber. The new rubber formed on incubation contained no long-chain fatty acid groups esterified to the rubber molecules, as is the case in in vivo Hevea rubber. These facts show the differences in the mechanism of initiation and termination between the in vitro and in vivo rubber formation reactions.