Magnesium ion regulation of in vitro rubber biosynthesis by Parthenium argentatum Gray

The rate of rubber biosynthesis and the molecular weight of the rubber produced are both strongly affected by [Mg 2+] in Parthenium argentatum. Natural rubber is produced by a rubber transferase (a cis-prenyltransferase). Rubber transferase uses allylic pyrophosphate to initiate the rubber molecule and isopentenyl pyrophosphate (IPP) to form the polymer. Rubber biosynthesis also requires a divalent metal cation. Understanding how molecular weight is regulated is important because high molecular weight is required for high quality rubber. We characterized the in vitro effects of Mg 2+ on the biosynthetic rate of rubber produced by an alternative natural rubber crop, Parthenium argentatum (guayule). The affinity of the rubber transferase from P. argentatum for IPP · Mg was shown to depend on the Mg 2+ concentration in a similar fashion to the H. brasiliensis rubber transferase, although to a less extreme degree. Also, in vitro Mg 2+ concentration significantly affects rubber molecular weight of both species, but molecular weight is less sensitive to Mg 2+ concentration in P. argentatum than in H. brasiliensis.