title: Thioglycoside hydrolysis catalyzed by beta-glucosidase.
abstract: Sweet almond beta-glucosidase (EC 3.2.1.21) has been shown to have significant thioglycohydrolase activity. While the Km values for the S- and O-glycosides are similar, the k(cat) values are about 1000-times lower for the S-glycosides. Remarkably, the pH-profile for k(cat)/Km for hydrolysis of p-nitrophenyl thioglucoside (pNPSG) shows the identical dependence on a deprotonated carboxylate (pKa 4.5) and a protonated group (pKa 6.7) as does the pH-profile for hydrolysis of the corresponding O-glycoside. Not surprisingly, in spite of the requirement for the presence of this protonated group in catalytically active beta-glucosidase, thioglucoside hydrolysis does not involve general acid catalysis. There is no solvent kinetic isotope effect on the enzyme-catalyzed hydrolysis of pNPSG.
authors.affiliation: Department of Chemistry, Tulane University, New Orleans, LA 70118, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Shen
authors.forename: Larry D
authors.initials: LD
authors.lastname: Byers
mesh_terms: D001665:Binding Sites; D001671:Biochemistry / Q000379:methods; D002021:Buffers; D002384:Catalysis; D002845:Chromatography; D004798:Enzymes / Q000737:chemistry; D006027:Glycosides / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D027861:Prunus / Q000201:enzymology; D013379:Substrate Specificity; D013865:Thioglycosides / Q000737:chemistry*; D001617:beta-Glucosidase / Q000378:metabolism*
chemical_list: D002021:Buffers; D004798:Enzymes; D006027:Glycosides; D013865:Thioglycosides; D001617:beta-Glucosidase