ATP-independent fatty acyl-coenzyme A synthesis from phospholipid - Coenzyme A-dependent transacylation activity toward lysophosphatidic acid catalyzed by acyl-coenzyme A : lysophosphatidic acid acyltransferase

CoA-dependent transacylation activity in microsomes is known to catalyze th e transfer of fatty acids between phospholipids and lysophospholipids in th e presence of CoA without the generation of free fatty acids. We previously found a novel acyl-CoA synthetic pathway, ATP-independent acyl-CoA synthes is from phospholipids. We proposed that: 1) the ATP-independent acyl-CoA sy nthesis is due to the reverse reaction of acyl-CoA:lysophospholipid acyltra nsferases and 2) the reverse and forward reactions of acyltransferases can combine to form a CoA-dependent transacylation system. To test these propos als, we examined whether or not recombinant mouse acyl-CoA:1-acyl-sn-glycer o-3-phosphate (lysophosphatidic acid, LPA) acyltransferase (LPAAT) could ca talyze ATP-independent acyl-CoA synthetic activity and CoA-dependent transa cylation activity. ATP-independent acyl-CoA synthesis was indeed found in t he membrane fraction from Escherichia coli cells expressing mouse LPAAT, wh ereas negligible activity was observed in mock-transfected cells. Phosphati dic acid (PA), but not free fatty acids, served as an acyl donor for the re action, and LPA was formed from PA in a CoA-dependent manner during acyl-Co A synthesis. These results indicate that the ATP-independent acyl-CoA synth esis was due to the reverse reaction of LPAAT, In addition, bacterial membr anes containing LPAAT catalyzed CoA-dependent acylation of LPA; PA but not free fatty acid served as an acyl donor. These results indicate that the Co A-dependent transacylation of LPA consists of 1) acyl-CoA synthesis hom PA through the reverse action of LPAAT and 2) the transfer of the fatty acyl m oiety of the newly formed acyl-CoA to LPA through the forward reaction of L PAAT.