Biosynthesis of the Methoxylated Carotenoids in Rhodospirillum rubrum

Abstract

The synthesis of the methoxylated carotenoids P481, OH-P481 and spirilloxanthin increases at a uniform rate during the log phase growth of R. rubrum. The synthesis of these pigments from methionine-methyl-C14 substantiates that spirilloxanthin is the terminal product of carotenoid conversions and that the mono-methoxylated pigments are synthesized prior to the di-methoxylated spirilloxanthin. The order of biosynthesis of these pigments from specific activity measurements is P481 - OH-P481 spirilloxanthin. The hydroxylated intermediate should be synthesized from P481 by the specific hydration of a double bond. Desaturation of OH-P481 followed by transmethylation of the (OH) group would lead to spirilloxanthin. Methoxyl carotenoids are synthesized from adenosyl-methionine in chromatophore preparations. Transmethylation of the hydroxyl intermediates by activated methionine in the bacterial carotenoids produces the methoxylated carotenoids.