Hydrolysis of novel diacylglycerol analogs and phorbol diesters by serum lipase.
Rat serum, active in the hydrolysis of the tumor-promoting phorbol diester, 12-O-tetradecanoylphorbol-13-acetate (TPA), was examined with regard to lipid interferences of [3H]TPA hydrolysis and enzyme substrate specificity. The enzymatic hydrolysis of TPA could be enhanced 8-fold, over crude serum, by using a lipid-free acetone powder of rat serum. Addition of lipid to the lipid-free acetone powder produced potent inhibition of TPA hydrolysis. The inclusion of multilamallar liposomes resulted in similar inhibition, and isolation of liposomes by high-speed centrifugation showed that 95% of the radiolabeled TPA was associated with the fatty pellet. Substrate specificity studies demonstrated that the serum activity hydrolyzes the long-chain ester of TPA and the long-chain primary acyl group of diacylglycerols. TPA was hydrolyzed at approximately twice the rate of dioleoylglycerol; however, the most reactive substrates were those synthetic analogs of diacylglycerol containing a short-chain ester group at the sn-2 position. Palmitic acid was liberated from [1-14C]palmitoyl-2-acetyl-sn-glycerol and [1-14C]palmitoyl-2-butyryl-sn-glycerol at 120- and 33-times the rate of TPA hydrolysis, respectively. Lipase resistant 1-hexadecyl-2-[3H]acetylglycerol was also used as substrate, but the sn-2 ester moiety showed poor lability. The diacylglycerol analogs are new lipase substrates and, in view of their similarities to the fatty acyl portion of TPA, it is thought that these compounds could serve as protein kinase C activators.
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D000818:Animals; D001769:Blood; D002855:Chromatography, Thin Layer; D004075:Diglycerides / Q000378:metabolism*; D005989:Glycerides / Q000378:metabolism*; D006868:Hydrolysis; D008049:Lipase / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008297:Male; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism; D010704:Phorbols / Q000378:metabolism*; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D013379:Substrate Specificity; D013755:Tetradecanoylphorbol Acetate / Q000378:metabolism*
D004075:Diglycerides; D005989:Glycerides; D008081:Liposomes; D010169:Palmitic Acids; D010704:Phorbols; D019308:Palmitic Acid; D011494:Protein Kinases; D011493:Protein Kinase C; D008049:Lipase; D013755:Tetradecanoylphorbol Acetate