Specificity of lipases is controlled by the molecular properties of the enzyme, structure of the substrate and factors affecting binding of the enzyme to the substrate. Types of specificity are as follows. I. Substrate: (a) different rates of lipolysis of TG, DG, and MG by the same enzyme; (b) separate enzymes from the same source for TG, DG and MG. II. Positional: (a) primary esters; (b) secondary esters; and (c) all three esters or nonspecific hydrolysis. III. Fatty acid, preference for similar fatty acids. IV. Stereospecificity: faster hydrolysis of one primary sn ester as compared to the other. V. Combinations of I-IV. Lipases with these specificities are: Ia, pancreatic; Ib, postheparin plasma. IIa, pancreatic; IIb, Geotrichum candidum, for fatty acids with cis-9-unsaturation, and IIc, Candida cylindracea. III, G. candidum for unsaturates. IV. sn-1, postheparin plasma and sn-3 human and rat lingual lipases. V. Rat lingual lipase. Methods for determination involve digestion of natural fats of known structure and synthetic acylglycerols followed by analysis of the lipolysis products. All of the types of specificity have been detected with use of synthetic acylglycerols. Detection of stereospecificity requires enantiomeric acylglycerols which are difficult to synthesize, so other methods have been developed. These involve the generation of 1,2-(2,3)DG and resolution of the enantiomers. Trioleoylglycerol or racemic TG can be used as substrates. If the lipase is stereospecific, then either the sn-1,2- or 2,3-enantiomer will predominate. The relative amounts of the enantiomers can be determined by measurement of specific rotation, and nuclear magnetic resonance spectra. The DG can also be separated by conversion to phospholipids and hydrolysis with phospholipases A-2 or C. Applications of these procedures are discussed and data on the specificity of various lipases presented.

The lingual lipase in gastric aspirates from premature infants was found to be partially stereospecific forsn‐3 esters of synthetic enantiometric triacylglycerols containing 18∶1 and 16∶0. Thesn‐3 ester was hydrolyzed about 4 times faster than the acid at thesn‐1 position with no difference in rates between 18∶1 and 16∶0. Thesn‐2 was also hydrolyzed to some extent.

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Gastric lipase activity in aspirates from premature human infants was tested for fatty acid and positional selectivity using racemic diacid triacylglycerols (TG) as substrates. The resulting free fatty acids and monoacylglycerols (MG) were recovered and analyzed. Octanoic acid (8:0) and decanoic acid (10:0) were hydrolyzed with a preference of 61.5:1 and 2.4:1 compared to palmitic acid (16:0) from rac-16:0-8:0-8:0 and rac-16:0-10:0-10:0, respectively. The ratio of lauric acid (12:0) to oleic acid (18:1) hydrolyzed from rac-18:1-12:0-12:0 was 13:1. Myristic acid (14:0), 18:1 and linoleic acid (18:2) were released at similar rates. These data and the composition of the MG suggest that, in vitro, the lipase is selective for shorter chain fatty acids and for fatty acids on the primary positions of the TG backbone.