title: A pH switch affects the steady-state kinetic mechanism of pyranose 2-oxidase from Trametes ochracea.
abstract: The flavin-dependent pyranose 2-oxidase catalyzes the oxidation of d-glucose and other pyranoses at the C2 atom to yield 2-keto-sugars and hydrogen peroxide. Here, the steady-state kinetic mechanism of the enzyme from Trametes ochracea was investigated as a function of pH. Our findings show that the enzyme follows a bi-bi ping-pong kinetic mechanism at pH values <7.0, and a bi-bi ordered mechanism at pH values >7.0. Thus, at low pH the reactivity of the reduced enzyme with oxygen is controlled a by a conformational change of the enzyme that is associated with the release of the 2-keto-sugar from the active site of the enzyme. In contrast, at high pH the reduced enzyme-product complex permits the reaction of oxygen with the flavin. The study also illustrates that caution should be exerted in extrapolating the conclusions drawn on steady-state kinetic mechanisms established at a single pH value to other pH's in flavoprotein oxidases.
authors.affiliation: Department of Chemistry, Georgia State University, Atlanta, 30302-4098, USA.
authors.forename: Kunchala
authors.initials: K
authors.lastname: Rungsrisuriyachai
authors.forename: Giovanni
authors.initials: G
authors.lastname: Gadda
mesh_terms: D002237:Carbohydrate Dehydrogenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007661:Ketoses / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D008958:Models, Molecular; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D055454:Trametes / Q000201:enzymology* / Q000235:genetics
chemical_list: D007661:Ketoses; D011994:Recombinant Proteins; C017022:glucosone; D002237:Carbohydrate Dehydrogenases; C022489:pyranose oxidase; D005947:Glucose