Dual Role of Methionine in the Biosynthesis of Diacylglyceryltrimethylhomoserine in Chlamydomonas reinhardtii

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Abstract
Biosynthesis of the polar group of diacylglyceryl-O-4′-(N,N,N-trimethyl)homoserine (DGTS) was studied in intact cells of Chlamydomonas reinhardtii Dangeard. Among the three C4 amino acids tested, only l-methionine could specifically inhibit the photosynthetic incorporation of [14C]NaHCO3 into the polar group of DGTS. The radioactivity in l-[14C]methionine, which was labeled at either the C3 + C4, the C1, or the methyl carbon, was efficiently incorporated into the polar group of DGTS. These results suggest that the C4 backbone and the S-methyl group of l-methionine are precursors to the C4 backbone and the N-methyl groups of DGTS, respectively.