title: Selective retention of essential fatty acids: the role of hepatic monoacylglycerol acyltransferase.
abstract: In the suckling rat, chick embryo, and hibernating marmot, fatty acids provide the major source of energy, and despite the high rate of hepatic beta-oxidation, these animals selectively retain long-chain polyunsaturated derivatives of C18:2n-6 and C18:3n-3. To determine whether the hepatic microsomal activity monoacylglycerol acyltransferase (MGAT) (EC 2.3.1.22) could provide a mechanism to selectively acylate monoacylglycerols that contain essential fatty acids, we tested the ability of MGAT activity from each of the three species to acylate sn-2-monoC18:1-, sn-2-monoC18:2-, sn-2-monoC18:3-, and sn-2-monoC20:4-glycerols. Hepatic MGAT activity acylated sn-2-monoC18:3-glycerol and sn-2-monoC18:2-glycerol in preference to sn-2-monoC18:1-glycerol in each of the three different lipolytic animals. MGAT's acyl group specificity could not be explained by invoking differences in membrane fluidity because the apparent affinity for sn-2-monoC20:4-glycerol was not increased. Further, sn-2-monoC18:3-glycerol remained a preferred substrate under assay conditions when both the C18:3 and C18:1 species were present in equal amounts. As would be predicted in the presence of high activity of a selective MGAT, the hepatic glycerolipids from neonatal rats showed increases in dienoic, trienoic, and C22:6 fatty acids and relative decreases in monoenoic, saturated, and C20:4 fatty acids. We hypothesize that, during lipolysis, the reacylation of sn-2-monoacylglycerols by MGAT may provide a mechanism by which essential fatty acids are retained within specific tissues.
authors.affiliation: Department of Nutrition, University of North Carolina at Chapel Hill 27599.
authors.forename: T
authors.initials: T
authors.lastname: Xia
authors.forename: N
authors.initials: N
authors.lastname: Mostafa
authors.forename: B G
authors.initials: BG
authors.lastname: Bhat
authors.forename: G L
authors.initials: GL
authors.lastname: Florant
authors.forename: R A
authors.initials: RA
authors.lastname: Coleman
mesh_terms: D000215:Acylation; D000217:Acyltransferases / Q000378:metabolism*; D000818:Animals; D000833:Animals, Suckling; D002144:Callithrix; D002642:Chick Embryo; D005227:Fatty Acids / Q000032:analysis; D005228:Fatty Acids, Essential / Q000378:metabolism*; D005989:Glycerides / Q000378:metabolism; D006605:Hibernation; D008055:Lipids / Q000737:chemistry; D008099:Liver / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism; D010743:Phospholipids / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D005227:Fatty Acids; D005228:Fatty Acids, Essential; D005989:Glycerides; D008055:Lipids; D010743:Phospholipids; D000217:Acyltransferases; C021802:2-acylglycerol O-acyltransferase