Natural rubber biosynthesis pathway in plants.

The monomer isopentenyl pyrophosphate (IPP) is derived from two sources: the mevalonic acid (MVA) pathway and the methylerythritol (MEP) pathway. IPP is converted to dimethylallyl pyrophosphate (DMAPP) by IPP-isomerase. DMAPP and IPP are then polymerized by cis-prenyltransferase (CPT) to form cis-1,4-polyisoprene, the main component of NR. The polymerization occurs on the surface of small rubber particles, which are coated with small rubber particle protein (SRPP). Some key enzymes of the MVA pathway are hydroxy methylglutaryl coenzyme A synthase (HMGS) and hydroxy methylglutaryl coenzyme A reductase (HMGR).