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

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 C(4) amino acids tested, only l-methionine could specifically inhibit the photosynthetic incorporation of [(14)C]NaHCO(3) into the polar group of DGTS. The radioactivity in l-[(14)C]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 C(4) backbone and the S-methyl group of l-methionine are precursors to the C(4) backbone and the N-methyl groups of DGTS, respectively.