Evidence for the specificity of esterase and lipase by the use of three chromogenic substrates.

Following the development of a histochemical method for demonstrating non-specific esterase (1) in tissue sections by enzymatic hydrolysis of Bnaphthyl acetate, the possibility was explored of developing a similar method for lipase together with convenient calorimetric methods for measuring the activity of both enzymes in blood serum. Interest in the enzymes which hydrolyze carboxylic esters stems from the discovery by Hanriot in 1896 (2) of an enzyme in serum and tissues which hydrolyzed monobutyrin. He called it “lipase,” a term which was immediately challenged (3, 4) on the ground that the serum does not hydrolyze true fats and that the enzyme is an esterase which splits the esters of the lower fatty acids. This difference of opinion still prevails (5-7). Presumably the ideal substrates for lipase are the glycerides of long chain fatty acids and for esterase the simple esters of short chain carboxylic acids. But a considerable degree of overlapping in enzymatic hydrolysis by these two enzymes occurs, since both enzymes can split esters of intermediate sized chains (8). The most effective hydrolysis which each enzyme produces (9,lO) depends more on the length of the acid chain than on the type of alcohol to which it is attached. Since the enzymes present in liver, kidney, and serum hydrolyze lower fatty acid esters quite readily and higher ones poorly, the action involved is considered to be due to esterase. Extracts of pancreas hydrolyze both types well and, therefore, probably contain both esterase and lipase (11). In order to study these differences further, so as to determine more precisely the specificity of these two enzymes with regard to short and long chain fatty acid esters and their relationship to certain enzymatic inhibitors and activators, the &naphthyl esters of acetic (CJ, lauric (C&J, and palmitic-stearic (CkC&) acids were prepared as substrates. Solutions or emulsions of these substrates were