Human pancreatic lipase study with bile salt activation and substrates from a homologous series of naphthyl alkanoates

Because sodium cholate proved to be a more reliable activator than sodium taurocholate for human serum lipase assay, a series of α-naphthyl alkanoates (of 8-, 9-, 10-, and 14-carbon acids), β-naphthyl alkanoates (of 8–16-carbon acids) and β-naphthyl alkenoates (of 2-nonenoic and 2-decenoic acids) were prepared and were studied for their sensitivity toward pancreatic lipase with cholate and taurocholate activation and in the presence of human serum. Maximal sensitivity to pancreatic lipase was found both in the α- and β-naphthyl nonanoates, suggesting that esters from acids of this chain length best meet the structural requirements for substrates for pancreatic lipase. Cholate proved a more reliable activator then taurocholate of the β-esters. β-Naphthyl nonanoate (βC9) was singled out for special study. Saturation of the enzyme (2 μg. pancreas/ml.) occurred at a substrate concentration of 0.2–0.25 mg./ml. leading to zero-order kinetics and hydrolysis rates directly proportional to enzyme concentration. Maximal incubation temperature for measurement of human pancreatic lipase in human serum was 37.5 °C. while that for pancreas alone was 45 °. Serum was observed to be a noncompetitive inhibitor of βC9. Some sera had more antilipase than others. Studies are now in progress on the use of βC9 for lipase assay. These studies may lead to better substrates and methods for histochemistry and for assay of human serum lipase activity.