title: Reducing sugars can induce the oxidative inactivation of rhodanese.
abstract: The enzyme rhodanese (thiosulfate sulfurtransferase, EC 2.8.1.1) is inactivated on incubation with reducing sugars such as glucose, mannose, or fructose, but is stable with non-reducing sugars or related polyhydroxy compounds. The enzyme is inactivated with (ES) or without (E) the transferable sulfur atom, although E is considerably more sensitive, and inactivation is accentuated by cyanide. Inactivation of E is accompanied by increased proteolytic susceptibility, a decreased sulfhydryl titer, a red-shift and quenching of the protein fluorescence, and the appearance of hydrophobic surfaces. Superoxide dismutase and/or catalase protect rhodanese. Inactive enzyme can be partially reactivated during assay and almost completely reactivated by incubation with thiosulfate, lauryl maltoside, and 2-mercaptoethanol. These results are similar to those observed when rhodanese is inactivated by hydrogen peroxide. These observations, as well as the cyanide-dependent, oxidative inactivation by phenylglyoxal, are explained by invoking the formation of reactive oxygen species such as superoxide or hydrogen peroxide from autooxidation of alpha-hydroxy carbonyl compounds, which can be facilitated by cyanide.
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760.
authors.forename: P M
authors.initials: PM
authors.lastname: Horowitz
authors.forename: M
authors.initials: M
authors.lastname: Butler
authors.forename: G D
authors.initials: GD
authors.lastname: McClure
mesh_terms: D005632:Fructose / Q000494:pharmacology*; D005947:Glucose / Q000494:pharmacology*; D006601:Hexoses / Q000494:pharmacology*; D007700:Kinetics; D008358:Mannose / Q000494:pharmacology*; D010084:Oxidation-Reduction; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013884:Thiosulfate Sulfurtransferase / Q000037:antagonists & inhibitors*; D013997:Time Factors
chemical_list: D006601:Hexoses; D005632:Fructose; D013884:Thiosulfate Sulfurtransferase; D005947:Glucose; D008358:Mannose