title: Comparison of acyl-oxyester and acyl-thioester lipids as substrates for bovine milk lipoprotein lipase.
abstract: The dithioester analog of dihexanoylphosphatidylcholine, rac-1,2-S,S-dihexanoyl-3-phosphocholine-1,2-dimercapto-3-propanol was synthesized and compared to the corresponding acyl-oxyester lipid as a substrate for bovine milk lipoprotein lipase. The apparent maximal reaction velocity (Vmax) for dihexanoyldithiophosphatidylcholine was considerably lower than that for dihexanoylphosphatidylcholine (0.12 vs. 5.0 mumol product released/min per mg lipoprotein lipase, respectively). The apparent Km values were 1.9 and 4.0 mM, respectively. 3-Butyrylthio-1,2-dibutyryloxypropane was also compared to tributyrylglycerol as a substrate for lipoprotein lipase; hydrolysis of the acyl-thioester bond was insignificant when compared to the corresponding oxyester derivative. Apolipoprotein C-II, the activator protein of lipoprotein lipase for long-chain fatty acyl substrates, had no effect on the hydrolysis of either the thio- or oxyester short-chain substrates. The low lipoprotein lipase activity for the thioester substrates is discussed in relation to the structure of the lipid and the active site of the enzyme.
mesh_terms: D000818:Animals; D002417:Cattle; D005260:Female; D006868:Hydrolysis; D007202:Indicators and Reagents; D007700:Kinetics; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008892:Milk / Q000201:enzymology*; D010713:Phosphatidylcholines / Q000138:chemical synthesis; D013379:Substrate Specificity
chemical_list: D007202:Indicators and Reagents; D010713:Phosphatidylcholines; C032166:1,2-hexanoylphosphatidylcholine; C042779:1,2-hexanoylthiophosphotidylcholine; D008071:Lipoprotein Lipase