An inducible intracellular β-glucosidase (EC 18.104.22.168) from Streptomyces sp. QM-B814 (ATCC 11238) has been purified and characterized. The purified polypeptide is monomeric with a relative molecular mass of 62 kDa by SDS-PAGE and 42 kDa by size-exclusion chromatography; its isoelectric point is 4.2. The difference in the molecular mass values can be attributed to the glycosylated nature of the protein. The purified enzyme has a pH optimum of 6.0-6.5. The temperature optimum for activity is 50°C; at this temperature the enzyme is stable for 1 h. The enzyme hydrolyzes mainly aryl-β-glucosides but also presents significant activity against β-linked disaccharides and maltose. The enzyme displays an unusual kinetic behavior and biphasic Lineweaver-Burk and Eadie-Hofstee plots for p-nitrophenyl-β-d-glucoside and cellobiose were obtained. The enzyme presents β-glycosyltransferase activity and an exoglycosidase-type action on cellodextrins. It is inhibited by δ-gluconolactone (Ki 0.44 mM) but, remarkably, glucose in the range 25-200 mM enhances the rate of p-nitrophenyl-β-d-glucoside hydrolysis. © 1995.
|Journal||Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology|
|Publication status||Published - 6 Sep 1995|
- Glucose-enhanced glucosidase