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Title: Tumor promoting phorbol diesters: substrates for diacylglycerol lipase

Enzyme activity in rat serum was examined utilizing the potent tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and various glycerolipids as substrates. The serum activity was specific for hydrolysis of the long chain tetradecanoate moiety of TPA, hydrolyzed mono- and diacylglycerols, but was not effective against triacylglycerols, cholesterylesters, or phospholipids. Heating the enzyme preparation at 56/sup 0/C for 1 min was dually effective in reducing the hydrolysis of both TPA and dioleoylglycerol by 83-86% of control levels. The potent diacylglycerol lipase inhibitor, RHC 80267, inhibited the hydrolysis of TPA in the 0.2-1.0 ..mu..M range and was also a potent blocker of monoacyl- and diacylglycerol hydrolysis. In substrate competition studies, exogenous unlabeled TPA was added to the (/sup 14/C)dioleoylglycerol-containing reaction mixture, however, this produced an approximate 3-fold stimulation of (/sup 14/)dioleoylglycerol hydrolysis. Although we have not established whether the hydrolysis of TPA and diacylglycerol is the work of one enzyme, the effectiveness of the specific lipase inhibitor, RHC 80267, demonstrates that diacylglycerol lipase can utilize TPA as substrate, a finding never before documented. This point is of interest in light of the theory that phorbol esters act by mimicry of the natural lipid mediator, diacylglycerols. 44 references, 3 figures, 1 table.
Authors:
Publication Date:
OSTI Identifier:
5871776
Resource Type:
Journal Article
Resource Relation:
Journal Name: Biochem. Biophys. Res. Commun.; (United States); Journal Volume: 123:1
Research Org:
Oak Ridge Associated Universities, TN
Country of Publication:
United States
Language:
English
Subject:
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.; LIPASE; ENZYME ACTIVITY; PHORBOL ESTERS; METABOLISM; BIOCHEMISTRY; CARBON 14 COMPOUNDS; ENZYME INHIBITORS; GLYCEROL; HYDROLYSIS; LIPIDS; RATS; SUBSTRATES; TEMPERATURE EFFECTS; TRACER TECHNIQUES; TUMOR PROMOTERS; ALCOHOLS; ANIMALS; CARBOXYLESTERASES; CARCINOGENS; CHEMICAL REACTIONS; CHEMISTRY; DECOMPOSITION; ENZYMES; ESTERASES; ESTERS; HYDROLASES; HYDROXY COMPOUNDS; ISOTOPE APPLICATIONS; LABELLED COMPOUNDS; LYSIS; MAMMALS; ORGANIC COMPOUNDS; PROMOTERS; RODENTS; SOLVOLYSIS; VERTEBRATES 560301* -- Chemicals Metabolism & Toxicology-- Cells-- (-1987)