Properties of a novel glucose-enhanced beta-glucosidase purified from Streptomyces sp. (ATCC 11238).
An inducible intracellular beta-glucosidase (EC 3.2.1.21) 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 degrees C; at this temperature the enzyme is stable for 1 h. The enzyme hydrolyzes mainly aryl-beta-glucosides but also presents significant activity against beta-linked disaccharides and maltose. The enzyme displays an unusual kinetic behavior and biphasic Lineweaver-Burk and Eadie-Hofstee plots for p-nitrophenyl-beta-D-glucoside and cellobiose were obtained. The enzyme presents beta-glycosyltransferase activity and an exoglycosidase-type action on cellodextrins. It is inhibited by delta-gluconolactone (Ki 0.44 mM) but, remarkably, glucose in the range 25-200 mM enhances the rate of p-nitrophenyl-beta-D-glucoside hydrolysis.
Pérez-Pons
J A
JA
Institut de Biologia Fonamental, Universitat Autònoma de Barcelona, Bellaterra, Spain.
Rebordosa
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X
Querol
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D000596:Amino Acids / Q000032:analysis; D005947:Glucose / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D007700:Kinetics; D008970:Molecular Weight; D013302:Streptomyces / Q000201:enzymology*; D013379:Substrate Specificity; D013696:Temperature; D001617:beta-Glucosidase / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism
D000596:Amino Acids; D001617:beta-Glucosidase; D005947:Glucose