Abstract
The activities of the proposed triacylglycerol synthetase complex, acyl-CoA ligase, acyl-CoA acyltransferase (AAT), monoacylglycerol acyltransferase (MGAT), and diacylglycerol acyltransferase (DGAT), coeluted upon Cibacron blue 3GA-agarose affinity chromatography of detergent-solubilized rat intestinal microsomes. The AAT activity is associated with a 54-kDa protein, that binds covalently an acyl group from acyl-CoA via a thiol ester linkage (Lehner, R. and Kuksis, A. (1993) J. Biol. Chem. 268, 24726-24733). Reagents that prevent the acyl-AAT formation inhibit triacylglycerol synthesis as does the removal of AAT from the complex by immunoprecipitation. In the absence of mono- and diacylglycerol acceptors, the acyl group is transferred to water. It is proposed that triacylglycerol synthesis proceeds via a sequential transfer of acyl groups from acyl-CoA ligase to the AAT, from which they are passed to the mono- and diacylglycerol acyltransferases for incorporation into the di- and triacylglycerols depending on the availability of the acyl acceptors.
Highlights
Richard Lehner-t and Arnis Kuksis§ From the Banting and Best Department of Medical Research, C
It is proposed that triacylglycerol synthesis proceeds via a sequential transfer of acyl groups from acyl-CoA ligase to the acyl-CoA acyltransferase (AAT), from which they are passed to the mono- and diacylglycerol acyltransferases for incorporation into the di- and triacylglycerols depending on the availability of the acyl acceptors
We report on the possible role of AAT in the triacylglycerol synthetase complex isolated by affinity chromatography
Summary
Vol 270, No 23, Issue of June 9, pp. 13630-13636, 1995 Printed in U.S.A. Triacylglycerol Synthesis by Purified Triacylglycerol Synthetase of Rat Intestinal Mucosa. The activities of the proposed triacylglycerol synthetase complex, acyl-CoA ligase, acyl-CoA acyltransferase (AAT) , monoacylglycerol acyltransferase (MGAT), and diacylglycerol acyltransferase (DGAT), coeluted upon Cibacron blue 3GA-agarose affinity chromatography of detergent-solubilized rat intestinal microsomes. It is proposed that triacylglycerol synthesis proceeds via a sequential transfer of acyl groups from acyl-CoA ligase to the AAT, from which they are passed to the mono- and diacylglycerol acyltransferases for incorporation into the di- and triacylglycerols depending on the availability of the acyl acceptors. The sequential intracellular reesterification of 2-monoacylglycerol to triacylglycerol has been proposed to be catalyzed by a triacyl-glycerol synthetase complex [2] consisting of MGAT,l DGAT, and of a fatty acid activating enzyme, acyl-Co.A ligase. The present study shows that a covalent binding of the acyl group by AAT is required for acylglycerol biosynthesis, since inhibition of acylation ofAAT prevents triacylglycerol biosynthesis.
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