Reverse Reaction of Lysophosphatidylinositol Acyltransferase

Abstract

CoA-dependent transacylation activity in microsomes catalyzes the transfer of fatty acid between phospholipids and lysophospholipids in the presence of CoA without the generation of free fatty acid. We examined the mechanism of the transacylation system using partially purified acyl-CoA:lysophosphatidylinositol (LPI) acyltransferase (LPIAT) from rat liver microsomes to test our hypothesis that both the reverse and forward reactions of acyl-CoA:lysophospholipid acyltransferases are involved in the CoA-dependent transacylation process. The purified LPIAT fraction exhibited ATP-independent acyl-CoA synthetic activity and CoA-dependent LPI generation from PI, suggesting that LPIAT could operate in reverse to form acyl-CoA and LPI. CoA-dependent acylation of LPI by the purified LPIAT fraction required PI as the acyl donor. In addition, the combination of purified LPIAT and recombinant lysophosphatidic acid acyltransferase could reconstitute CoA-dependent transacylation between PI and phosphatidic acid. These results suggest that the CoA-dependent transacylation system consists of the following: 1) acyl-CoA synthesis from phospholipid through the reverse action of acylCoA:lysophospholipid acyltransferases; and 2) transfer of fatty acyl moiety from the newly formed acyl-CoA to lysophospholipid through the forward action of acylCoA:lysophospholipid acyltransferases.The fatty acyl moieties of phospholipids are not static but instead are dynamically turned over. Acyltransferases and transacylases catalyze the acylation of lysophospholipids and are involved in the biosynthesis and fatty acid remodeling of phospholipids (1-4). A CoA-dependent transacylation system (or CoA-dependent transacylase) catalyzes the transfer of fatty acids from phospholipids to lysophospholipids in the presence of CoA without generation of free fatty acids (5-11). In rabbit liver microsomes, arachidonic acid (20:4n-6), linoleic acid (18: 2n-6), and stearic acid (18:0), esterified in phospholipids, are the main species transferred to lysophospholipids in the presence of CoA, indicating that this system shows some fatty acid specificity (11). Phosphatidylcholine (PC), 1 phosphatidylethanolamine (PE), and phosphatidylinositol (PI) have been shown to serve as donor phospholipids, PI being the preferred acyl donor (10, 11). Despite the importance of CoA-dependent transacylation system in fatty acid remodeling of phospholipids, the mechanism underlying the transacylation system is not fully understood yet. In fact, the identities of the enzymes responsible for CoA-dependent transacylation reactions have not been established. Although we and other investigators (5,6,11,(12)(13)(14) considered previously that acyl-CoA:lysophospholipid acyltransferases may be involved in CoA-dependent transacylation reactions, direct and conclusive evidence has not been obtained because of the lack of success in purification and cloning of membrane-bound lysophospholipid acyltransferases and transacylases, including the CoA-dependent transacylation system.Previously, we de...

Coenzyme-A-Independent Transacylation System; Possible Involvement of Phospholipase A2 in Transacylation

“…The K m for CoA in the CoA-dependent transacylation reaction is very low (1–4 μM), suggesting that the reaction proceeds in the presence of physiological levels of CoA. We have proposed that the CoA-dependent transacylation reaction is mediated by a combination of reverse and forward reactions of acyl-CoA:lysophospholipid acyltransferases [7,8,23,24,25,26,27]. …”

The contributions of biosynthesis and acyl chain remodelling to the molecular species profile of phosphatidylcholine in yeast

“…Alternatively, acyl chain shuffling via transacylation may occur in which another phospholipid serves as acyl chain donor and a lyso-phospholipid as the acceptor (see e.g. [28]). Both acyl-CoAdependent and acyl-CoA-independent acylation of lyso-PC have been reported in yeast [29,30].…”

Roles of C-Terminal Processing, and Involvement in Transacylation Reaction of Human Group IVC Phospholipase A2 (cPLA2γ)

“…Several types of transacylation system are known, including CoA-dependent and independent systems. We have already proposed a partial mechanism for a CoA-dependent transacylation system that combines the reverse and forward reactions of acyl-CoA:lysophospholipid acyltransferases, based on examination of lysophosphatidic acid acyltransferase and lysophosphatidylinositol acyltransferase (7,8).…”

“…CoA-independent transacylases or transacylation systems catalyze the transfer of fatty acids esterified at the sn-2 position of phospholipids to various lysophospholipids in the absence of any cofactors (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). Of particular interest is the role of these enzymes in the arachidonic acid mobilization between phospholipids and 1-O-alkyl-sn-glycero-3-phosphocholine (GPC)(lyso platelet activating factor).…”