Adenosyl-methionine incorporation into the methoxylated carotenoids in chromatophores of Rhodospirillum rubrum.

Abstract
The carotenoid methyl transferase(s) which is responsible for the formation of C14-methoxylated carotenoids from S-adenosyl-methionine-methyl-C14 is present in chromatophores of R. rubrum. The enzymic syntheses of the methoxylated carotenoids in chromato-phores from adenosyl-methionine-methyl-C14 and the syntheses of these carotenoids in growing cells from methionine-methyl-C14 is similar. The transmethylation reaction which accounts for the incorporation of the methyl group of adenosyl-methionine into spirilloxanthin is linear with time and requires an -SH group for maximal activity. The optimal rate of transmethylation occurs in chromatophores isolated from 46 hr. cultures.