Inhibitory activity of pyridindolol on beta-galactosidase

The activity of pyridindolol in inhibiting beta-galactosidases obtained from various sources has been studied. Whereas acid bovine liver beta-galactosidase (optimal pH 4.0) was not affected by this compound, neutral bovine liver beta-galactosidase (pH-optimum = 7.0) was inhibited by pyridindolol in reaction mixtures of pH 4.0 approximately 5.0. There was no inhibition at pH 7.0. The type of inhibition is non-competitive by formation of a pyridindolol-enzyme complex. Since beta-galactosidases from other sources are not affected by pyridindolol, the inhibitory action of this compound seems to be rather specific for neutral bovine liver beta-galactosidase.