Synthetic reaction of Cellvibrio gilvus cellobiose phosphorylase.

The synthetic reactions of the cellobiose phosphorylase from Cellvibrio gilvus were investigated in detail. It was found that, besides D-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 D-glucose. The enzyme showed higher activity with beta-D-glucose than with the alpha-anomer as an acceptor. This result indicates that it recognizes the anomeric hydroxyl group not involved directly in the reaction. beta-D-Cellobiose was also phosphorolyzed faster than the alpha-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 alpha-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.