Measurement and study of substrate specificity of exoglucosidase activity in eutrophic water.

The alpha- and beta-glucosidase activity in natural samples can be readily measured during short incubation times (20 min) by using the artificial substrates 4-methylumbelliferyl-alpha-d-glucoside and 4-methylumbelliferyl-beta-d-glucoside. The apparent K(m) of both alpha- and beta-glucosidase for these respective substrates is 0.01 muM. The homologous disaccharides maltose and cellobiose competitively inhibit alpha- and beta-glucosidase, respectively. Absolute substrate specificity of the alpha- and beta-glucosidase is observed with respect to the configuration of carbon atoms 1 and 4. Enrichment cultures on either alpha- and beta-glucoside result in increasing activity of the corresponding glucosidase, both in absolute terms and with respect to the other glucosidase.