Double reciprocal plots of the phosphorolysis of cellobionic acid catalyzed by SdCBAP. The initial velocities of the phosphorolytic reaction were determined with a combination of initial concentrations of CbA (0.5, 1.0, 2.0, and 3.0 mm) and Pi (open circles, 0.1 mm; filled circles, 0.2 mm; open squares, 0.3 mm; filled squares, 0.5 mm; open triangles, 1.0 mm; filled triangles, 2.0 mm).