INTRODUCTION
Lipases (EC 3.1.1.3) are a class of hydrolases that are primarily responsible for the hydrolysis of acylglycerides. They are ubiquitous and indispensable for the bioconversion of lipids (triacylglycerol) in nature. In addition to their biological significance, lipases hold tremendous potential for exploitation in biotechnology. They possess the unique feature of acting at the aqueous and non aqueous interface which distinguishes them from esterases. The concept of lipase interfacial activity evolved from restriction of their catalytic activity to interface between lipid and water. The catalytic activity of lipases depends largely on the aggregated state of substrates. Experimental evidences suggest that the activation involves unmasking and structuring of enzyme-active site, through conformational changes, that require presence of oil-in water droplets. Recent studies on the structure of several lipases have provided some clues for understanding their hydrolytic activity, interfacial activation and stereoselectivity of lipases. Enzymes such as proteases and carbohydrases have been used industrially for a number of years and corner the largest share of the world wide enzyme market. Whilst lipases at present account for less than 5% of the market, this share has the potential to increase dramatically via a wide range of different applications. The lipases catalyze wide range of reactions, including hydrolysis, inter-esterification, alcholysis, acidolysis, esterification and aminolysis. They catalyse the hydrolysis of fatty acid ester bond in the triacylglycerol (TAG) and release free fatty acids (ffa). The reaction is reversible; the direction of the reaction depends upon the water content available in the reaction. In low water media lipases catalyse esterification, transesterification and interesterification. Biochemical and molecular characterization of a number of lipases of different sources has brought to light great deal of heterogeneity in them with regard to specificity, amino acid sequence and catalytic properties. Based on the inhibition of their enzyme activity by chemical modification, lipases were initially classified as serine hydrolases. Serine present at their active site has been shown to be enclosed in the highly conserved domain and represents the only common feature shared by all determined lipases sequenced so far. Although lipases can be produced easily on a large scale by growing microorganisms in a fermentor, yet their use was, till recently confined largely to oleo-chemistry and dairy based industry. However the last quarter of the 20th century has witnessed unprecedented use of lipases in biotechnology, manufacture of pharmaceuticals and pesticides, single cell protein production, biosensor preparation and in waste management etc. Lipases have become an integral part of the modern food industry and are used in the preparation of a variety of products including fruit juices, baked food, vegetable fermentation and dairy enrichment. They are also used in leather industry for processing hides and skins (bating) and for treatment of activated sludge and other aerobic waste products where they remove the thin layer of the fats and by so doing provide for oxygen transport. The lipid digesting preparation is employed in sewage disposal plants in USA under the trade name lipase M-Y (Meito Sangyo Co., Nagoya Japan). Lipases may also assist in the regular performance of anaerobic digesters. Nearly 1000 tonnes of lipase are used annually in detergent industry, primarily as lipid stain digesters. They also are used as flavour development agents in the preparation of cheese, butter and margarine. These hydrolases are endowed with substrate specificity that surpasses any known enzyme. This property confers to them the potential that is literally boundless. The growing interest in lipases is reflected by publication of an average of 1000 research papers per year, on different aspects of these enzymes. Some of the common sources of lipases are tabulated in Table 1.
Pancreatic lipase of porcine origin is one of the earliest recognized and is still the best known lipase. Plant lipases are not used commercially; the animal and microbial lipases are used extensively. The most important source of animal lipase is the pancreas of cattle, sheep, hogs and pigs. The disadvantage with pancreatic (/animal) lipases is that they cannot be used in the processing of vegetarian or kosher food. Also, that these extracts contain components which have undesirable effect. The pig pancreatic extract contains trypsin, which produces bitter tasting amino acids. They are also likely to contain residual animal viruses, hormones, etc. Microbes are major source of the 100 or so enzymes produced industrially for reasons mentioned above.
TABLE 1. Source Mammalian
Name Human Pancreatic Lipase Pig Pancreatic Lipase Guinea Pig Pancreatic Lipase Rhizomucormeihei Pencilliumcamberti Humicolalanuginosa Rhizopusoryzae Aspergillus niger Candida rugosa Candida antarctica Lipase A Candida antarctica Lipase B Geotrichiumcandidum Chromobacteriumviscosum Pseudomonas cepacia Pseudomonas aeruginosa Pseudomonas fluorescens Pseudomonas fragi Bacillus thermocatenulatus Staphylococcus hyicus
Fungal
Bacterial
