Regulation of rubber biosynthetic rate and molecular weight in Hevea brasiliensis by metal cofactor

Metal ion cofactors are necessary for prenyltransferase enzymes. Magnesium and manganese can be used as metal ion cofactor by rubber transferase (a cis-prenyltransferase) associated with purified rubber particles. The rubber initiation rate, biosynthetic rate, and molecular weight produced in vitro from Hevea brasiliensis rubber transferase is regulated by metal ion concentration. In addition, K-m(IPP.Mg) varies significantly with [Mg2+].K-m(IPP.Mg) decreases from 8000 +/- 600 muM at [Mg2+] = 4 mM to 68 +/- 10 muM at [Mg2+] = 8 mM and increases back to 970 +/- 70 muM at [Mg2+] = 30 mM. The highest affinity of rubber transferase for IPP.Mg occurred when [Mg2+] = A(max) (metal concentration that gives highest IPP incorporation rate). A metal ion is required for rubber biosynthesis, but an excess of metal ions interacts with the rubber transferase inhibiting its activity. The results suggest that H. brasiliensis could use [Mg2+] as a regulatory mechanism for rubber biosynthesis and molecular weight in vivo.