There have been many attempts to rationalize the correlation between enzyme activity and the nature of organic solvents. Conventional wisdom dictates that water is required for enzyme action. This conclusion originates from the fact that water participates (directly or indirectly) in all non-covalent interactions maintaining the native, catalytically active enzyme conformation [94, 95]. Hence, the complete removal of water should drastically distort that conformation and inactivate the enzyme. Although this reasoning is undoubtedly correct, the real question is whether water is indeed required but how much water is crucial to retain the catalytic activity of lipase. As long as this water is present around the enzyme molecules, the rest of water can probably be replaced with an organic solvent without adversely affecting the performance of the enzyme. Since the absolute amount of water present in a few monolayers is very small, this situation is as good as to an enzyme functioning in a nearly anhydrous organic medium. Stability of lipases in organic solvents makes their uses commercially feasible in the enzymatic esterification reactions [96&#;99].
As far as the conformational properties and functioning of lipases in organic solvents is concerned, lipases were found to be fit because of their rigid conformation and interfacial activation characteristics. Many lipases are active in organic solvents where they catalyze a number of useful reactions including esterification [100&#;102]. Various factors for maintaining lipase activity in non-aqueous media have been considered such as tuning up of the lipases by pH and it is accomplished while the enzyme is dissolved in the buffer prior to dehydration (lyophillization) before its suspension in organic solvent. Also the correct protonation state of the side chain of amino acids residues of lipase is important for retaining its catalytic activity [103]. A relevant practical example is the use of esterses and lipases to catalyze esterifications in organic solvents such as isopropyl acetate, ethyl ferulate, isopropyl ferulate and butyl ferulate [104&#;106]. Enzymatic reactions in organic media are actually divided into two systems: reactions performed in organic solvent systems and in solvent-free systems. The solvent-free system, i.e. the reaction mixture comprising only liquid organic substrates (such as liquid oil) without any organic solvent, if it is possible, has high volumetric performance and economic advantages over the organic solvent system especially for large scale production. It is also desirable for the synthesis of food-grade products since very stringent safety regulations concerning organic solvent usage have to be observed in food industry. Non aqueous enzymology is concerned with the utilization and understanding of enzymes in essentially organic environments. Conventional biocatalysis is carried out in aqueous media, and it is not surprising that most of the methods developed to study enzymes performance are water based.
But day by day the interest has been focused on using enzymes to catalyze reactions in organic media [107]. If an enzyme could function in an essentially organic environment, increased ease of product recovery, increased hydrophobic reactant solubility and reduced microbial contamination would be properties contributing to its wide applicability. Altering the solvent can have a dramatic effect on enzyme function. Also lyophilized enzyme powders suspended in organic solvents could catalyze a variety of novel catalytic functions e.g. esterification, transesterification, interesterification etc. The exclusion of water leads to an improved enzyme thermostability (as water is a reactant in many processes that irreversibly denature enzymes) and the reduction of undesirable side reactions that require water as a substrate [108]. There has been much interest in the development of rules to predict the effects of various solvents on the biocatalyst [109]. A good correlation was found between the ester mole fraction at equilibrium and log P of the solvent. The equilibrium constant for esterification correlates well with solubility of water in the organic solvents. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of n-octanol-water partition (log P) coefficient; electron pair acceptance index or the polarizability [40]. When log P <2, distortion of water structure occurs; if 2< log P <4, the effect of solvent is unpredictable and if log P >4, water structure is intact. Although the equilibrium position for lipase-catalyzed esterification reactions is independent of the enzyme, it is interesting to note that it is not independent of solvent [110]. The hydrophobic solvents yielded higher reaction rates than the hydrophilic ones even at a constant water activity; however, better enantio-selectivity was observed [111]. Enzymatic methods of ester synthesis are more effective when performed in non-aqueous media [112].
Other Name(s):
Lipasa, Triacylglycerol Lipase.
Lipase is a digestive enzyme that is found in many plants, animals, bacteria, and molds. An enzyme is a protein that speeds up a particular biochemical reaction in the body. People use lipase as a medicine.
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Lipase is used for indigestion, heartburn, allergy to gluten in wheat products (celiac disease), Crohn's disease, and cystic fibrosis.
Lipase seems to work by breaking down fat into smaller pieces, making digestion easier.
More evidence is needed to rate the effectiveness of lipase for these uses.
Lipase seems to be safe for most people. It can cause some side effects such as nausea, cramping, and diarrhea.