| Research Abstract |
Various lipases (pancreatic lipase, caroxylester lipase, Pseudomonas fluorescens lipase and lipoprotein lipase) were purified on a large scale using thc PSLC chromatography system. The synthesis/hydrolysis of esters was studied in an aqueous solution using these purified lipases. When oleic acid and hexadecanol emulsified with gum araubic were incubated with these lipases at neutral pH, ester Was synthesized, in dose- and time-dependent manner, and the apparent equilibrium ratio of palmityl olcate/oleic acid was about 0.9/0.1. These lipase catalyzed the hydrolysis of palmityl oleate emulsified with gum arabic, and the apparent equilibrium ratio of palmityl oleate/free oleic acid also about 0.9/0.1. The equilibrium ratio was affected by the incubation pH and the alcohol chain length. When incubation pH was below pH 7.0 , the equilibrium ratio favored ester formation. The equilibrium ratio decreased sharply at alkaline pH (above pH 8.0). The ratio also deceased when fatty alcohols with acyl chains shorter than dodecanol were used. When trioleoylglycerol/hexadecanol emulsion was incubated with these lipases, palmityl oleate was synthesized in a dose- and time-dependent fashion. The lipase also synthesized retinyl ester from fatty acid and retinol, and diacylgycerol from fatty acid and monoacylglycerol. These results suggest that lipase catalyzes ester formation through an acyl-enzyme intermediate. The acyl-enzyme is deacylated by nucleophilic attack of various alcohols such as simple aliphatic alcohols, retinol, monoacylglycerol and water. Therefore, we might name the lipase "acyltransferase". These finding can be applied to understanding the mechanism of some water insoluble ester formations by lipase at various sites.
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