Hydrolysis of phospholipids by purified milk lipoprotein lipase - Effect of apoprotein CII, CIII, A and E, and synthetic fragments

Different pyrene-labeled phospholipid monolayer vesicles were used as subst rates for the bovine milk lipoprotein lipase activity. The effects of synth etic fragments of apoprotein C II were measured on the hydrolysis of 1-myri stoyl-2[9(1pyrenyl)-nonanoyl] phosphatidylcholine in vesicles: The activati ng capacity of fragments 30-78 and 43-78, 50-78 and 55-78, compared to enti re apo CII, were similar to that, obtained with hydrolysable triglycerides. Our study shows that the longer the carboxy terminal fragment is, the high er is the activation. The phospholipid hydrolysis activity represents in th e presence of apo C II, 36% of the triglycerides hydrolysis activity. Phosp holipid hydrolysis is less dependent on activator than triglycerides hydrol ysis (100% and 300% of increase with apo CII for phosphatidyl-choline and t riglycerides respectively). The ratio hydrolysis without apo C II/hydrolysi s with apo CII was different when other phospholipids than myrystoyl-phospa tidylcholine were assayed: phosphatidyl-serine, ethanolamine, -choline, -gl ycerol, or diglycerides and butanoylglycerols. Fragment CIII1 (1-40) which did not bind to lipids, had no inhibitory effect. The entire sugar moiety a nd the first 40 amino acids are not required for the total inhibition of LP L. Inhibition was also obtained with Apo A I, A II,C I and fragments of apo E. (C) 2000 Elsevier Science B.V. All rights reserved.