title: The specificity of α-glucosidase from Saccharomyces cerevisiae differs depending on the type of reaction: hydrolysis versus transglucosylation.
abstract: Our investigation of the catalytic properties of Saccharomyces cerevisiae α-glucosidase (AGL) using hydroxybenzyl alcohol (HBA) isomers as transglucosylation substrates and their glucosides in hydrolytic reactions demonstrated interesting findings pertaining to the aglycon specificity of this important enzyme. AGL specificity increased from the para(p)- to the ortho(o)-HBA isomer in transglucosylation, whereas such AGL aglycon specificity was not seen in hydrolysis, thus indicating that the second step of the reaction (i.e., binding of the glucosyl acceptor) is rate-determining. To study the influence of substitution pattern on AGL kinetics, we compared AGL specificity, inferred from kinetic constants, for HBA isomers and other aglycon substrates. The demonstrated inhibitory effects of HBA isomers and their corresponding glucosides on AGL-catalyzed hydrolysis of p-nitrophenyl α-glucoside (PNPG) suggest that HBA glucosides act as competitive, whereas HBA isomers are noncompetitive, inhibitors. As such, we postulate that aromatic moieties cannot bind to an active site unless an enzyme-glucosyl complex has already formed, but they can interact with other regions of the enzyme molecule resulting in inhibition.
authors.affiliation: Faculty of Chemistry, University of Belgrade, Studentski trg 12, 11000, Belgrade, Serbia.
authors.forename: Veličković
authors.initials: V
authors.lastname: Dušan
authors.forename: Milosavić
authors.initials: M
authors.lastname: Nenad
authors.forename: Bezbradica
authors.initials: B
authors.lastname: Dejan
authors.forename: Bihelović
authors.initials: B
authors.lastname: Filip
authors.forename: Ann Marie
authors.initials: AM
authors.lastname: Segal
authors.forename: Segan
authors.initials: S
authors.lastname: Dejan
authors.forename: Trbojević
authors.initials: T
authors.lastname: Jovana
authors.forename: Dimitrijević
authors.initials: D
authors.lastname: Aleksandra
mesh_terms: D006868:Hydrolysis; D007700:Kinetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013379:Substrate Specificity; D000520:alpha-Glucosidases / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000520:alpha-Glucosidases