title: Lipid-lipid interactions as regulators of carboxylester lipase activity.
abstract: The hydrolysis of 1,3-dioleoylglycerol and related substrates by mammalian pancreatic carboxylester lipases was studied. Mixed lipid films of substrates with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine at the argon-buffer interface were exposed to relatively high levels of monomeric porcine pancreatic carboxylester lipase for a brief period. With either 1,3-dioleoylglycerol, 1,2-dioleoylglycerol, trioleoylglycerol, or oleoylmethanol as a substrate, the percentage of substrate hydrolysis increased abruptly from near zero to near 100% with increasing proportion of substrate in the film. The phospholipid was not hydrolyzed. Using 1,3-dioleoylglycerol as the substrate with either the dimeric, porcine pancreatic carboxylester lipase, human pancreatic carboxylester lipase, or human milk bile salt-stimulated lipase gave results identical to those obtained with the porcine monomer. Hydrolysis of 1,3-dioleoylglycerol by porcine monomeric carboxylester lipase was independent of the initial surface pressure of the film. However, a strong correlation was observed between hydrolysis and interfacial lipid composition at all surface pressures, even if bulk 1,3-dioleoylglycerol was also present. The ultrasensitive dependence of hydrolysis on interfacial lipid composition, i.e. lipid-lipid interactions, suggests that such "switching" may contribute to the regulation of diacylglycerol levels in cells where they function in signal transduction.
authors.affiliation: Hormel Institute, University of Minnesota, Austin 55912.
authors.forename: T
authors.initials: T
authors.lastname: Tsujita
authors.forename: J M
authors.initials: JM
authors.lastname: Muderhwa
authors.forename: H L
authors.initials: HL
authors.lastname: Brockman
mesh_terms: D000818:Animals; D043182:Carboxylesterase; D002265:Carboxylic Ester Hydrolases / Q000302:isolation & purification / Q000378:metabolism*; D005260:Female; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008895:Milk, Human / Q000201:enzymology*; D010179:Pancreas / Q000201:enzymology*; D010189:Pancreatic Juice / Q000201:enzymology*; D011312:Pressure; D013379:Substrate Specificity; D013499:Surface Properties; D013552:Swine
chemical_list: D002265:Carboxylic Ester Hydrolases; D043182:Carboxylesterase