Abstract
It has recently been reported that immobilized enzymes or chemically modified enzymes can enhance the thermostability of an enzyme. In this study, we prepared lipase, α-chymotrypsin and subtilisin carlsburg modified by citraconic anhydride and then compared their thermostability with those of free enzymes. The activities of the lipase, α-chymotrypsin and subtilisin carlsburg were determined by monitoring the rates of hydrolysis of tri-n-butyrin, N-acetyl-L-tyrosine ethyl ester and Suc-Ala-Ala-Pro-Phe-pNA, respectively. The chemically modified lipase had higher thermostabilty compared with free lipase and less loss of the activity compared with free lipase. The half-life of modified lipase prolonged 3 times as great as that of free one. Modified α-chymotrypsin was partially lost its activity although its thermostability was enhanced compared with that of free one. In the case of modified subtilisin carlsburg, the appreciable enhancement of thermostability is not observed. The mechanism of deactivation of these enzymes followed a two-step series model. Enzymatic reaction at higher temperature was possible with the lipase modified by citraconic anhydride, resulting in higher conversion rate.
