Fatty acyl chain specificity of phosphatidylcholine hydrolysis catalyzed by lipoprotein lipase. Effect of apolipoprotein C-II and its (56-79) synthetic fragment.
Mixed acyl chain phosphatidylcholine molecules in Triton N-101 micelles were employed as substrates for lipoprotein lipase to test which substrate acyl chain has the greatest effect on activation of the enzyme by apolipoprotein C-II. The phospholipase A1 activity of lipoprotein lipase was measured by pH-stat. The activation factor (lipoprotein lipase activity plus apolipoprotein C-II/activity minus apolipoprotein C-II) increased monotonically with apolipoprotein C-II concentration up to 1 microM apolipoprotein C-II at an enzyme concentration of 0.01 microM. The maximal activation factor for phosphatidylcholine substrate molecules with sn-2 acyl chain lengths of 14 averages 14.8. By contrast, for sn-2 acyl chain lengths of 16 the activation factor was 29.2. Varying the sn-1 acyl chain length had no significant effect on the activation factor. The chain-length dependence of the activation factor is similar with the apolipoprotein C-II peptide fragment comprising residues 56-79, which does not include the lipid-binding region of apolipoprotein C-II. These data are consistent with a model for activation of lipoprotein lipase in which residues 56-79 bind to lipoprotein lipase and alter the interaction of the sn-2 acyl chain of the phosphatidylcholine (PC) substrate or the lysoPC product within the activated state complex.
D053304:Apolipoprotein C-II; D001056:Apolipoproteins C / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005227:Fatty Acids / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D008071:Lipoprotein Lipase / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000378:metabolism*; D013379:Substrate Specificity
D053304:Apolipoprotein C-II; D001056:Apolipoproteins C; D005227:Fatty Acids; D010446:Peptide Fragments; D010713:Phosphatidylcholines; D008071:Lipoprotein Lipase