Biosynthesis of diacylglyceryl-N,N,N-trimethylhomoserine in Rhodobacter sphaeroides and evidence for lipid-linked N methylation.
Rhodobacter sphaeroides, which produces diacylglyceryl-N,N,N-trimethylhomoserine (DGTS) under phosphate-limiting conditions, was incubated with L-[1-14C]- and L-[methyl-14C]methionine in pulse and pulse-chase experiments. The label was incorporated specifically into the polar part of DGTS and of three other compounds. One of them (compound 3) could be identified as diacylglyceryl-N,N-dimethylhomoserine by cochromatography with a reference obtained semisynthetically from DGTS. It was labelled when using L-[1-14C]- as well as L-[methyl-14C]methionine as a precursor and was converted to DGTS when incubated with the DGTS-forming eukaryotic alga Ochromonas danica (Chrysophyceae). Of the other two compounds labelled with L-[1-14C]methionine, compound 2 was also labelled with L-[methyl-14C]methionine whereas compound 1 was not, suggesting that these two intermediates are the corresponding N-methyl and nonmethylated lipids, respectively. The methyltransferase inhibitor 3'-deazaadenosine enhanced the amounts of compounds 1 to 3 but decreased the amount of DGTS. It is concluded that in R. sphaeroides, DGTS is synthesized by the same pathway as in eukaryotic organisms and that the N methylation is the terminal step in this process and occurs on the preformed lipid. Since the phosphatidylcholine-deficient mutant CHB20, lacking the phosphatidylcholine-forming N-methyltransferase was able to synthesize DGTS, one or several separate N-methyltransferases are suggested to be responsible for the synthesis of DGTS.
Institut fur Biochemie der Universität Bern, Switzerland.
M
M
Hofmann
W
W
Eichenberger
D002250:Carbon Radioisotopes; D056890:Eukaryota / Q000378:metabolism; D050356:Lipid Metabolism; D008715:Methionine / Q000493:pharmacokinetics; D008745:Methylation / Q000187:drug effects; D008780:Methyltransferases / Q000037:antagonists & inhibitors; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D014280:Triglycerides / Q000096:biosynthesis* / Q000737:chemistry; D014372:Tubercidin / Q000494:pharmacology
C021660:1(3),2-diacylglyceryl-3(1)-O-4'-(N,N,N-trimethyl)homoserine; D002250:Carbon Radioisotopes; D014280:Triglycerides; D008715:Methionine; D008780:Methyltransferases; D014372:Tubercidin