Lipases

Abstract

Lipases are water-soluble, ester hydrolases that are traditionally defined by their marked preference for apolar, water-insoluble ester substrates. This group of enzymes also includes species referred to as cholesterol esterases. Lipases and cholesterol esterases are distinguished from phospholipases that catalyze the hydrolysis of acyl ester bonds of highly amphipathic phospholipids having an sn-glycero-3-phospho-X moiety and from carboxylesterases that hydrolyze polar, water-soluble esters. These distinctions are relative, however, because some lipases exhibit activity toward phospholipids or soluble esters. Typical natural lipase substrates include, in order of amphipathicity, long aliphatic chain acyl esters of cholesterol (cholesteryl esters), triacyl esters of glycerol (triacylglycerols), acyl esters of long chain alcohols (wax esters), diacyl esters of glycerol (diacylglycerols), and monoacyl esters of glycerol. Because lipase substrates tend to be oily and only weakly amphipathic, they reside primarily in a bulk oil phase in preference to the aqueous phase or to the interface, that is, monomolecular surface phase that separates the bulk oil and aqueous phases. It follows, because lipases are water-soluble enzymes, that the site of lipolysis is the quasi-two-dimensional interface. The focus of basic research on lipases has been to understand how a reaction involving such a change in dimensionality can occur and how it is regulated. Medically, lipases are targets for therapeutic intervention in the treatment of obesity. The focus of applied research with lipases has been to exploit the unusual properties of lipolytic systems for the production of chiral pharmaceuticals, improved detergents, and designer fats.