Phosphorolytic Reaction of Cellvibrio gilvus Cellobiose Phosphorylase

Cellobiose phosphorylase was purified from Cellvibrio gilvus cells by the method reported previously with some modifications, and its kinetic properties were studied in detail. The initial velocity of the synthetic reaction was 1.4 times as fast as that of the phosphorolytic one. The equilibrium constant of the phosphorolysis was 0.32 at 37°C and pH 7.0. No D-[U-(14)C]glucose exchange reaction was observed in the absence of Pi. Kinetic studies on the phosphorolytic reaction showed that the reaction follows an ordered bi bi mechanism. These results make a sharp contrast to those of sucrose phosphorylase, which catalyzes fructose exchange reaction and follows a ping pong bi bi mechanism. Kinetic parameters were calculated as KmA = 2.6 mM, KmB = 0.61mM, and KiA = 6.8 mw (A, D-cellobiose; B, Pi).