Characterization of acyl-coenzyme A:diacylglycerol acyltransferase (DGAT) enzyme of human small intestine
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ORIGINAL PAPER
Characterization of acyl-coenzyme A:diacylglycerol acyltransferase (DGAT) enzyme of human small intestine Yasushi Hiramine & Toshizumi Tanabe
Received: 20 September 2010 / Accepted: 22 December 2010 / Published online: 8 January 2011 # University of Navarra 2011
Abstract Acyl-coenzyme A:diacylglycerol acyltransferase (DGAT) enzyme plays a significant role in dietary triacylglycerol (TAG) absorption in the small intestine. However, the characteristics of human intestinal DGAT enzyme have not been examined in detail. The aim of our study was to characterize the human intestinal DGAT enzyme by examining acylCoA specificity, temperature dependency, and selectivity for 1,2-diacylglycerol (DAG) or 1,3-DAG. We detected DGAT activity of human intestinal microsome and found that the acyl-CoA specificity and temperature dependency of intestinal DGAT coincided with those of recombinant human DGAT1. To elucidate the selectivity of human intestinal DGAT to 1,2-DAG or 1,3-DAG, we conducted acyl-coenzyme A:monoacylglycerol acyltransferase assays using 1or 2-monoacylglycerol (MAG) as substrates. When 2MAG was used as acyl acceptor, both 1,2-DAG and TAG were generated; however, when 1-MAG was
used, 1,3-DAG was predominantly observed and little TAG was detected. These findings suggest that human small intestinal DGAT, which is mainly encoded by DGAT1, utilizes 1,2-DAG as the substrate to form TAG. This study will contribute to understand the lipid absorption profile in the small intestine. Keywords Human intestine . DGAT . Triacylglycerol . Diacylglycerol Abbreviations DGAT Acyl-coenzyme A:diacylglycerol acyltransferase MGAT Acyl-coenzyme A:monoacylglycerol acyltransferase TAG Ttriacylglycerol DAG Diacylglycerol MAG Monoacylglycerol
Introduction Y. Hiramine (*) Dainippon-Sumitomo Pharma Co., Ltd., 3-1-98 Kasugade-naka, Konohana-ku, 554-0022 Osaka, Japan e-mail: [email protected] T. Tanabe Department of Bioengineering, Graduate School of Engineering, Osaka City University, 3-3-138 Sugimoto-cho, Sumiyoshi-ku, 558-8585 Osaka, Japan
Triacylglycerol (TAG), a neutral lipid normally found in lipid droplets, is an important molecule for energy storage and lipid metabolism in animals [7]. TAG is synthesized by two major pathways, the glycerol 3phosphate pathway and the monoacylglycerol pathway [1]. In the glycerol 3-phosphate pathway, diacylglycerol (DAG) is synthesized by dephosphorylation of phosphatidic acid, and in the monoacylgly-
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cerol pathway, DAG is formed directly from monoacylglycerol (MAG) and fatty acyl-coenzyme A by acyl-coenzyme A:monoacylglycerol acyltransferase (MGAT). Both pathways share the final step in converting DAG to TAG, a reaction catalyzed by acyl-coenzyme A:diacylglycerol acyltransferase (DGAT), which is a rate-limiting enzyme for TAG synthesis. The monoacylglycerol pathway is best known for its role in fat absorption in the small intestine because of the high influx of MAG from breakdown of dietary TAG. In the intestine of animals, TAG contained in dietary fat is digested b
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