Biosynthesis of phospholipids in Clostridium butyricum: kinetics of synthesis of plasmalogens and the glycerol acetal of ethanolamine plasmalogen.
The biosynthesis of the plasmalogen forms of phosphatidylethanolamine (plasmenylethanolamine) and phosphatidylglycerol (plasmenylglycerol) and of the glycerol acetal of plasmenylethanolamine has been studied in cultures of Clostridium butyricum IFO 3852. When growing cells were pulsed with [32P]orthophosphate, there was a lag of 5 to 7 min between the rapid incorporation of label into the acylphosphatides and the rapid incorporation of label into the corresponding plasmalogens. The labeling of the glycerol acetal of plasmenylethanolamine was even slower. In pulse-chase experiments with 32Pi, the kinetics of labeling indicated precursor-product relationships between phosphatidylethanolamine and plasmenylethanolamine and between the latter and its glycerol acetal. A precursor-product relationship was also seen between phosphatidylglycerol and cardiolipin, but the kinetics of labeling of the alkenyl-containing forms of these lipids were not consistent with direct precursor-product relationships with the acyl lipids. In the presence of hydroxylamine and 32Pi, both phosphatidylserine and plasmenylserine accumulated 32P in a ratio of ca. 15:1. Upon release of the inhibition of phosphatidylserine decarboxylase, label appeared in the following sequence: phosphatidylethanolamine, plasmenylethanolamine, and the glycerol acetal of plasmenylethanolamine. Acyl phosphatidylglycerol was identified as a major phospholipid (17% of lipid phosphorus) in C. butyricum grown in low-phosphate (1.13 mM) medium with 50 mM Tris buffer. Of the acyl phosphatidylglycerol, 13% was acid labile. There appear to be two plasmalogen forms of acyl phosphatidylglycerol. One of these has a single alkenyl ether group, and the other has alkenyl ether groups on both glycerols.