Dependence upon pH of steady-state parameters for the beta-galactosidase-catalysed hydrolyses of beta-D-galactopyranosyl derivatives of different chemical types.

The effect of pH upon the beta-galactosidase-catalyzed hydrolyses of aryl galactosides is essentially similar for each of the three steps of their hydrolysis. It differs markedly from that on the hydrolysis of galactosyl pyridinium salts; these proceed through a 'non-bottleneck' pathway. While pH increase abolishes the rate of every step of the reaction for aryl galactosides, it favors the first step of hydrolysis of the galactosyl pyridinium salts, which supports the hypothesis that catalysis of these compounds originates largely in non-covalent interactions.