Binding specificity and reactivity studies on a broad-specificity β-glycosidase from porcine kidney

A broad-specificity β-glycosidase from porcine kidney was purified to homogeneity. Sodium dodecyl sulfate – polyacrylamide gel electrophoresis showed that it had a monomeric molecular weight of 55 000–60 000. Gel filtration showed a native molecular weight of about 115 000. These data imply that the native enzyme is a dimer. The enzyme can catalyze the hydrolysis of β bonds between glycosides and 4-methylumbelliferone or nitrophenol yielding D-fucopyranose, D-galactopyranose, D-glucopyranose, D-xylopyranose, and D-mannopyranose and of α bonds to yield L-arabinopyranose. This is the first study that shows a mammalian broad-specificity cytosolic β-glycosidase carrying out a reaction with a β-D-mannopyranoside. The nature of the broad specificity was studied with inhibitors. Similar inhibitor constants were found regardless of whether the substrate was a β-D-glucopyranoside or a β-D-galactopyranoside, so the enzyme probably has only one binding site with a broad specificity. The enzyme prefers to bind compounds with an axial hydroxyl at the 2 position and an equatorial hydroxyl at the 4 position; the 3 position does not affect binding significantly. The hydroxyl at the 6 position affects binding, but binding at that position depends on the configurations at the 2 and 4 positions. Thus, there must be some interactions between these three positions (2, 4, and 6). Lactones are also good inhibitors and this may relate to strain effects.