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  • Title: Altered positional specificity of human plasma lecithin-cholesterol acyltransferase in the presence of sn-2 arachidonoyl phosphatidyl cholines. Mechanism of formation of saturated cholesteryl esters.
    Author: Subbaiah PV, Liu M, Bolan PJ, Paltauf F.
    Journal: Biochim Biophys Acta; 1992 Sep 22; 1128(1):83-92. PubMed ID: 1390880.
    Abstract:
    The positional specificity of purified human lecithin-cholesterol acyltransferase (LCAT) was studied by analyzing the labeled cholesteryl ester (CE) species formed in the presence of proteoliposome substrates containing mixed chain phosphatidylcholine (PC) species, labeled cholesterol and apoprotein A-I. Whereas over 90% of the acyl groups used for CE synthesis were derived from the sn-2 position of most of the naturally occurring PC substrates, about 75% of the CE species formed in the presence of sn-1-myristoyl 2-arachidonoyl PC, sn-1-palmitoyl-2-arachidonoyl (PAPC) and sn-1-palmitoyl 2-docosahexaenoyl PC were derived from the sn-1-position. On the other hand, rat LCAT utilized mostly sn-2-acyl group from either PAPC or from sn-1-palmitoyl 2-linoleoyl PC. The positional specificity of the human enzyme was not affected by the alteration in the matrix fluidity, type of the apoprotein activator used, or by the free cholesterol/PC ratio in the substrate. These results show that the positional specificity of human plasma LCAT is altered in the presence of sn-2-arachidonoyl PC, or sn-2-docosahexaenoyl PC, probably due to steric restrictions at the active site, and this may account for the formation of disproportionately high concentrations of saturated CE, and low concentrations of long-chain polyunsaturated CE in human plasma, relative to the composition of sn-2-acyl groups in plasma PC.
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