Synthetic Reaction of Cellvibrio gilvus Cellobiose Phosphorylase

Abstract

The synthetic reactions of the cellobiose phosphorylase from Cellvibrio gilvus were investigated in detail. It was found that, besides n-glucose, some sugars having substitution or deletion of the hydroxyl group at C2 or C6 of the D-glucose molecule could serve as a glucosyl acceptor, though less effectively than n-glucose. The enzyme showed higher activity with β-D-glucose than with the α-anomer as an acceptor. This result indicates that it recognizes the anomeric hydroxyl group not involved directly in the reaction. β-D-Cellobiose was also phosphorolyzed faster than the α-anomer. Substrate inhibition was observed with D-glucose, 6-deoxy-D-glucose, or D-glucosamine as an acceptor, with D-glucose being most inhibiting. This inhibition was studied in detail and it was found that D-glucose competes with α-D-glucose-1-phosphate for its binding site. A model of competitive substrate inhibition was proposed, and the experimental data fit well to the theoretical values that were calculated in accordance with this model.