STUDY OF THE NEW ELECTRON-TRANSFER MEDIATORS IN GLUCOSE-OXIDASE CATALYSIS

The steady-state oxidation of glucose oxidase from Aspergillus niger by phenothiazines, phenoxazines, Wurster's salts, dithia- and tetrathiaaromatic compounds, and nickelocene was investigated spectrophotometrically and electrochemically. At pH 7.0 the determined oxidation rate constants (TN/K(m)) vary in the range 10(3) to 10(8) M-1 . s-1. For phenothiazines, phenoxazine and Wurster's salts oxidation constants depend on the redox potential of the electron acceptors, and results were interpreted in the framework of the outer sphere electron transfer theory (Marcus and Sutin, Biochim. Biophys. Acta, 811 (1985) 265). The interpretation of the kinetic results concerning thiaaromatic compounds and metallocenes are complicated due to complex formation with the enzyme active center and aggregation of their oxidized form in buffer solution.