Chemical Modification of Histidyl Residue in the Active Site of Brewer's Yeast α-glucosidase II

Abstract

α-Glucosidase II from brewer's yeast was inactivated by photooxidation in the presence of rose bengal at pH 6.8. Addition of substrate diminished the rate of inactivation. During photoinactivation the Michaelis constant was unchanged, but the maximumvelocity decreased with a decrease in residual activity. Anamino acid analysis of the oxidized enzymeshowed the reduction of two histidines and the cysteine residues.
Inactivation of the α-glucosidase II by diethylpyrocarbonate was also observed. One histidyl residue was modified, but tyrosyl and cysteinyl residues were not affected. The loss of activity of the modified enzyme was restored by treatment with hydroxylamine.
These results suggest that at least one histidyl residue serves a catalytic function in brewer's yeast α-glucosidase II.