Substrate specificity of the human splenic non-specific soluble beta-glucosidase

The soluble non-specific 4-methylumbelliferyl-beta-D-glucosidase, one of the three splenic groups previously reported [Maret, A., Salvayre, R., Nègre, A., and Douste-Blazy, L. (1981) Eur. J. Biochem. 115, 455-461], was partially purified by gel filtration and heat-inactivation (which inactivated the contaminating acid beta-galactosidase). Its substrate specificity was accurately demonstrated by comparing the enzymic properties towards each substrate and two-substrate mixed assays: 4-methylumbelliferyl beta-D-galactopyranoside, beta-D-glucopyranoside, beta-D-fucopyranoside, alpha-L-arabinopyranoside and beta-D-xylopyranoside (relative rates 100, 95, 70, 15, 5, respectively in the standard conditions used) were competitively hydrolysed. Information about the enzymic site was given by the effect of various substrate analogs: generally we observed a greater inhibition of beta-galactosidase activity than beta-glucosidase and beta-fucosidase activities. Moreover, p-nitrophenyl-beta-D-mannopyranoside showed a strong inhibitory effect on the three main activities of this enzyme, similar to D-glucono-1,5-lactone inhibition. A selective inhibition by Triton X-100 on beta-D-galactosidase activity and in a lesser degree on beta-D-fucosidase activity was discussed. The non-specific soluble beta-glucosidase from a Gaucher patient and from normal subjects showed identical properties. Thus this enzyme is not affected by the mutation in the Gaucher type I spleen.