Effects of both shortening and lengthening the active site nucleophile of Bacillus circulans xylanase on catalytic activity

The position of the two carboxyl groups in Bacillus circulans xylanase has an important effect on its catalytic action. Mutagenesis of the catalytic nucleophile Glu78 helps to change the distance between the two groups. The rate of glycosylation reduces drastically due to an increase in the separation. Catalytic activity reduces to a lesser degree when there is a decrease in the separation. The rate differences are not reflected in the extent of bond cleavage or proton donation at the transition state. Removal of the carboxyl group (Glu78Cys) stops catalytic activity.