LIPASE-CATALYZED BIOCHEMICAL REACTIONS IN NOVEL MEDIA - A REVIEW

Lipids in biological matter are mostly triacylglycerols (TAG). Lipolyt ic enzymes, primarily lipases, are indispensable for bioconversion of such lipids from one organism to another and within the organisms. In addition to their biological significance, lipases are very important in the field of food technology, nutritional and pharmaceutical scienc es, chemical and detergent industries, and clinical medicine because o f their ability to catalyze Various reactions involving a wide range o f substrates. Conventionally, lipases have been viewed as the biocatal ysts for the hydrolysis of TAG (fats and oils) to free fatty acids, mo noacylglycerols (MAG), diacylglycerols (DAG), and glycerol. The main a dvantages of lipase catalysis are selectivity, stereospecificity, and mild reaction conditions. Despite these advantages and the fact that e nzymatic splitting of fats for fatty acid production was described as early as in 1902 the lipase-catalyzed process has not replaced the com mercial physicochemical process for the continuous splitting of TAG ut ilizing super-heated steam. The limited exploitation of lipase technol ogy may be attributed to high enzyme cost, large reaction volume, requ irement for emulsification of substrate, and risk of microbial contami nation. Many of these limitations originate from the fact that lipases are employed mainly in water-rich reaction media where the solubility of the substrate TAG is very small. To circumvent this problem and to realize the full potential of lipase, researchers have explored newer approaches by manipulating the conditions under which the lipases Bet . Many of these novel approaches for lipase catalysis have been the ou tcome of the discovery that enzymes can be active in water-poor, non-p olar media (Hanhan, 1952; Misiorowski and Wells, 1974; Zaks and Kliban ov, 1984). Also, the finding that lipases can act in organic solvents has led to an expansion of their applicability in a wide variety of ch emical reactions. Lipase catalysis in some of the well established rea ction media has previously been reviewed (Brockerhoff and Jensen, 1974 ; Brockman, 1984; Lilly et al., 1987; Halling, 1990; Inada et al., 199 0; Malcata et at, 1990). The present review is intended to present a c ompilation and comparison of novel reaction systems used for lipase ca talysis. This review describes briefly the general characteristics of lipase reactions, applications of lipase in various fields, and conven tional lipase technology. The lipase-mediated biochemical reactions, p articularly the hydrolysis of TAG in novel reaction media is discussed in greater detail.