Transphosphatidylation activity in Clostridium butyricum. Evidence for a secondary pathway by which membrane phospholipids may be synthesized and modified.

Membrane particles from Clostridium butyricum, incubated with Triton X-100 and 32P-labeled phosphatidylethanolamine, phosphatidylglycerol, or phosphatidylserine, resulted in the labeling of three phospholipids. These unknown phospholipids incorporated label from the phosphate and acyl chains of the substrate, but not from the head group. Two-dimensional TLC of the intact lipids and their deacylation products showed that these lipids were phosphatidic acid, cardiolipin, and the previously unreported phosphatidyltriton. The reaction involved the transfer of the phosphatidyl moiety of the substrate molecule in a phospholipase D-like manner. The reaction displayed sigmoidal kinetics, did not require divalent cations, possessed an acidic pH optimum, and was sensitive to thermal inactivation. Differences in thermal sensitivity and pH optimum indicated that a distinct enzyme activity may be involved in the formation of cardiolipin. A primary alcohol group was required on the acceptor molecule, which could be either amphipathic or water-soluble. Addition of exogenous unlabeled phosphatidylglycerol resulted in the increased formation of cardiolipin, with a concomitant decrease in the level of phosphatidyltriton formed. Labeled phosphatidylethanolamine, phosphatidylglycerol, or phosphatidylserine could be formed upon addition of their corresponding alcoholic head group to incubations containing a 32P-labeled phosphatidyl donor and Triton X-100. These results indicate that, in C. butyricum, enzymic steps exist that would allow remodeling of the membrane phospholipids, without requiring de novo biosynthesis.