PURPOSE:To make esterase have excellent resistance to organic solvent without losing activity even in a highly concentrated organic solvent by chemically modifying esterase with introducing a specific group into amino group of esterase using a specific ester. CONSTITUTION:Esterase is dissolved in a buffer solution and a necessary amount of ester expressed by formula I (R is benzyloxy group, tertiary butoxy group, 9-fluorenylmethoxy group, p-methoxybenzyloxy group or 1-24C alkyl group) as a chemical modifier is added, then reacted to introduce RC(O)-group (R is same as the above) into 20-60% amino group to total amount of amino group in esterase. Next, modified enzyme is treated by an usual method such as gel filtration or membrane treatment and enzyme fraction is recovered after finish of the reaction, then subjected to freezing preservation or freezing drying to afford modified esterase. Thereby, enzyme-hydrolysis of ester is made possible by using said esterase. Furthermore, said esterase has excellent resistance to organic solvent.
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