Endocannabinoids and diacylglycerol kinase activity
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Mammalian diacylglycerol kinases are a family of enzymes that catalyze the phosphorylation of diacylglycerol to produce phosphatidic acid. The extent of interaction of these enzymes with monoacylglycerols is the focus of the present study. Because of the structural relationship between mono- and diacylglycerols, one might expect the monoacylglycerols to be either substrates or inhibitors of diacylglycerol kinases. This would have some consequence to lipid metabolism. One of the lipid metabolites that would be affected is 2-arachidonoyl glycerol, which is an endogenous ligand for the CB1 cannabinoid receptor. We determined if the monoglycerides 2-arachidonoyl glycerol or 2-oleoyl glycerol affected diacylglycerol kinase activity. We found that 2-arachidonoyl glycerol is a very poor substrate for either the epsilon or the zeta isoforms of diacylglycerol kinases. Moreover, 2-arachidonoyl glycerol is an inhibitor for both of these diacylglycerol kinase isoforms. 2-oleoyl glycerol is also a poor substrate for these two isoforms of diacylglycerol kinases. As an inhibitor, 2-oleoyl glycerol inhibits diacylglycerol kinase ε less than does 2-arachidonoyl glycerol, while for diacylglycerol kinase ζ, these two monoglycerides have similar inhibitory potency. These results have implications for the known role of diacylglycerol kinase ε in neuronal function and in epilepsy since the action of this enzyme will remove 1-stearoyl-2-arachidonoylglycerol, the precursor of the endocannabinoid 2-arachidonoyl glycerol.
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