Biosynthesis of rubber.

The problem of how rubber is synthesized in the plant has been divided into two portions: (i) the nature of the monomer used and how this monomer is synthesized, and (ii) the nature of the polymerization reaction by which the monomer is transformed to rubber. With respect to the first, the monomer appears to be the 5-carbon branched-chain compound beta-methylcrotonic acid or a derivative thereof. This substance is synthesized in the plant from acetyl-coA. With respect to the second, no information is available, since polymerization of the 5-carbon monomer units to polymers has not yet been achieved outside the living plant.