Regulation of initiation and polymer molecular weightof cis-1,4-polyisoprene synthesized in vitro by particlesisolated from Parthenium argentatum (Gray)

Natural rubber (NR) biosynthesis: perspectives from polymer chemistry

“…importantly, they demonstrated that increasing the amount of iPP while keeping the FPP concentration constant resulted in increased MW in three different types of WrPs: Hevea, guayule and Ficus elastica (Fig. 2.17) (Castillón and Cornish, 1999;Cornish et al, 2000). These findings support the notion of a living-like polymerization.…”

“…her group determined the MW of in vitro nr by means of dual-labeled liquid scintillation spectrometry (ss) (Castillón and Cornish, 1999). By introducing both radioactive iPP monomer and FPP initiator into in vitro nr biosynthesis, an average MW of newly-formed rubber could be calculated from a ratio between the 14 C-labeled monomer and the 3 h-labeled initiator Cornish, 1999, Cornish et al, 2000).…”

Molecular Cloning and Characterization of Rubber Biosynthetic Genes from Taraxacum koksaghyz

“…Natural rubber is composed of cis-1,4 polyisoprene with molecular weights ranging from <50 kDa in Ficus elastica to >1,000 kDa in H. brasiliensis (Cornish 1993;Castillón and Cornish 1999;Cornish et al 2000). Rubber biosynthesis takes place on the surface of rubber particles and is catalyzed by rubber-particle-bound cis-prenyltranferases (CPTs) via cis-1,4-polymerization of isoprene monomers derived from isopentenyl diphosphate (IPP).…”

Natural Rubber Biosynthesis and Physic-Chemical Studies on Plant Derived Latex

“…However, the varying size of the natural rubber product was shown not to be solely dependant on the rubber transferase. Through in vitro studies measuring the incorporation of labeled allylic diphosphate and IPP into isolated rubber particles from H. brasiliensis, P. argentatum and Ficus spp., it was demonstrated that the concentration of these two substrates determine the initiation of new natural rubber molecules and for this reason also the termination of chain elongation (Castillon and Cornish, 1999). In general, if IPP supply is limited, with an increasing concentration of FPP, more FPP is incorporated into rubber particles, inducing the initiation of new natural rubber molecules and simultaneously leading to a decrease in molecular mass of natural rubber molecules.…”

“…Analysis of the internal concentrations of FPP, IPP and Mg 2+ could reflect the correlation between rubber molecular mass and rubber transferase activity since the FPP to IPP ratio and the Mg 2+ concentration were in the optimal range for the specific rubber transferase in surveyed species (da Costa et al, 2005). Therefore, it was stated that these are the main factors for high molecular mass of natural rubber molecules in H. brasiliensis and P. argentatum (Castillon and Cornish, 1999;Kang et al, 2000b;Scott et al, 2003;da Costa et al, 2006). Next to sufficient supply of substrate and metal co-factor for rubber transferase activity, additional proteins appear to be involved in rubber biosynthesis.…”