Rat small-intestinal β-galactosidases. Influence of pH on the hydrolysis of different substrates

The influence of pH and the kind of buffer on the hydrolysis of lactose and four hetero-beta-galactosides (phenyl beta-galactoside, o-nitrophenyl beta-galactoside, p-nitrophenyl beta-galactoside and 6-bromo-2-naphthyl beta-galactoside) by homogenates of rat small-intestinal mucosa has been studied. 2. There are at least two beta-galactosidases present in the homogenates, one with optimum pH3-4 and another with optimum pH5-6. 3. The enzyme with the lower pH optimum is mainly a heterogalactosidase. It hydrolyses lactose slowly. The other enzyme is mainly a disaccharidase, since it hydrolyses lactose much more rapidly than the heterogalactosides. 4. Under the conditions used, citrate had an inhibitory effect on the 6-bromo-2-naphthyl beta-galactosidase activity at pH3-4, but did not influence the 6-bromo-2-naphthyl beta-galactosidase activity at pH5-6 or the hydrolysis of the other substrates at any pH.