Acyltransferases and transacylases involved in fatty acid remodeling of phospholipids and metabolism of bioactive lipids in mammalian cells.

Over 100 different phospholipid molecular species are known to be present in mammalian cells and tissues. Fatty acid remodeling systems for phospholipids including acyl-CoA: lysophospholipid acyltransferases, CoA-dependent and CoA-independent transacylation systems and lysophospholipase/transacylase are involved in the biosynthesis of these molecular species. Acyl-CoA:1-acyl-2-lysophospholipid acyltransferase prefers polyunsaturated fatty acyl-CoAs as acyl donors while acyl-CoA:2-acyl-1-lysophospholipid acyltransferase prefers saturated fatty acyl-CoAs. Therefore, the acyl-CoA:lysophospholipid acyltransferase system is involved in the synthesis of the phospholipid molecular species containing sn-1 saturated and sn-2 unsaturated fatty acids. The CoA-dependent transacylation system catalyzes the transfer of fatty acids esterified in phospholipids to lysophospholipids in the presence of CoA without the generation of free fatty acids. The CoA-dependent transacylation reaction in rat liver exhibits strict fatty acid specificity, i.e., three types of fatty acids (20:4, 18:2, and 18:0) are transferred. On the other hand, the CoA-independent transacylase catalyzes the transfer of C20 and C22 polyunsaturated fatty acids from diacyl phospholipids to various lysophospholipids, in particular, ether-containing lysophospholipids, in the absence of any cofactors. The CoA-independent transacylase is assumed to be involved in the accumulation of polyunsaturated fatty acids in ether-containing phospholipids and in the removal of deleterious ether-containing lysophospholipids. These acyltransferases and transacylases are involved in not only the remodeling of fatty acids but also the synthesis and degradation of some bioactive lipids and their precursors. In this review, the properties of these fatty acid remodeling systems and their possible roles in the biosynthesis of bioactive lipids are described.