Diradylglycerols Alter Fatty Acid Inhibition of Monoacylglycerol Acyltransferase Activity in Triton X-100 Mixed Micelles
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- 作者：Rosalind A. Coleman ; Ping Wang ; and B. Ganesh Bhat
- 刊名：Biochemistry
- 出版年：1998
- 出版时间：April 28, 1998
- 年：1998
- 卷：37
- 期：17
- 页码：5916 - 5922
- 全文大小：87K
- 年卷期：v.37,no.17(April 28, 1998)
- ISSN：1520-4995
文摘
The activity of hepatic monoacylglycerolacyltransferase (MGAT) (EC 2.3.1.22), a developmentally expressed microsomal enzyme, is inhibited by long-chain fattyacids, and stimulated by its product1,2-diacyl-sn-glycerol. Because the quantities of fattyacids and diacylglycerols are likely to vary inmembranes during different physiological conditions and could therebyalter MGAT activity, we examinedtheir combined effects on MGAT in Triton X-100/phospholipid mixedmicelles. MGAT's product, 1,2-diC18:1-sn-glycerol, which is also normally a cooperativeactivator of the activity, reversed the 50%inhibition caused by 10 mol % oleic acid. The presence of oleicacid also allowed low concentrations(<10 mol %) of 1,2-diC18:1-sn-glycerol to stimulate MGATactivity without the lag that is observed inthe absence of fatty acid. At 12.6 mol %,1,2-monoC18:1-sn-glycerol ether, which alone has no effectonMGAT activity, became an activator in the presence of 10 mol % oleicacid. Kinetic studies revealedthat in the presence of 15 mol % oleic acid,1,2-diC18:1-sn-glycerol ether increased the apparentVmax by3.8-fold while minimally altering the apparentKm for palmitoyl-CoA. Other neutral lipidsincluding tri-C18:1-glycerol, ceramide, and cholesterol oleate did not stimulate MGATin either the presence or theabsence of fatty acid. Assay conditions altered MGAT's apparentrelative preferences for potentialmonoradylglycerol substrates. The presence of phospholipids and ofMGAT's 1,2-diacyl-sn-glycerolproduct increased the enzyme's apparent preference for its2-monoacyl-sn-glycerol substrate by selectivelyincreasing the apparent Vmax 2.7-fold only when2-monoC18:1-sn-glycerol was the substrate. Thus,inaddition to previously reported regulation of MGAT by phospholipids andintracellular lipid secondmessengers, these studies lend additional support to the hypothesisthat changes in other membrane-associated lipids, such as long-chain fatty acids and diradylglycerols,may also profoundly alter the activityof MGAT.