THE SPECIFICITY OF PANCREATIC LIPASE FOR THE PRIMARY HYDROXYL GROUPS OF GLYCERIDES

Abstract

There are conflicting reports in the literature on the specificity of pancreatic lipase. Desnuelle (1) has summarized the evidence that pancreatic lipase hydrolyzes esters of long chain, but not short chain, fatty acids. Moreover, the enzyme under normal conditions acts only on glycerol esters. The question as to whether lipase has any specificity which depends on the location of the fatty acid on the glyceride molecule has never been answered satisfactorily. Until this question is answered satisfactorily, it will be impossible to demonstrate any specificity which the enzyme may have for particular long chain fatty acids. Weber and King (2) reported that the land 2-monoglycerides of lauric, myristic, palmitic, and stearic acids were hydrolyzed by pancreatic lipase at practically the same rate. Similarly Artom and Zummo (3), using 2-palmitoyl dicaprylin or 2-capryloyl dipalmitin as the substrate, found no difference in the rate of hydrolysis of the fatty acids esterified with the primary or secondary hydroxyl groups of glycerol. On the other hand, Balls and Matlack (4) investigated the enzymatic hydrolysis of the stearic acid esters of a number of primary, secondary, and tertiary alcohols. They concluded that the enzyme was specific for primary hydroxyl groups. Shortly thereafter Cedrangolo and Del Regno (5) reported that unsymmetrical diolein is hydrolyzed more rapidly than symmetrical diolein, thus indicating a lack of enzyme specificity for esters of primary alcohols. When the free hydroxyl groups of lor 2-monostearin were blocked with methyl groups joined to the glycerol by an ether linkage and these materials were used as the substrate, no marked group specificity was found, although the primary ester was hydrolyzed somewhat more rapidly than the secondary ester (6). The specificity of lipase for the primary hydroxyl groups of glycerides is indicated by the recent report of Borgstrom (7). When unlabeled triglyceride was digested in the presence of labeled free fatty acid, only the 1 and 3 positions of the glycerides came into equilibrium with the free fatty acids. None of the above studies, except that of Borgstrom, was based on compounds which could be considered typical of the usual edible triglycerides. Consequently, it was of interest to determine the course of lipase hydroly-