Mechanistic study of the autoxidation of reduced flavin and quinone compounds

• DOI: 10.1016/s0022-0728(97)00520-2
• Publication Date: 2002-07-25T12:39:37Z
• Authors: Hirosuke Tatsumi; Hiroshi Nakase; Kenji Kano; Tokugi Ikeda
• Keywords: 0301 basic medicine; 0303 health sciences; 03 medical and health sciences

The mechanism of the autoxidation of reduced flavin and quinone compounds was investigated through semiquantitative analysis of voltammetric waves of the reduction of dioxygen (O2) catalyzed by flavin and quinone adsorbed on electrode surfaces, where the redox equilibrium among the oxidized, (flavo)semiquinone and fully reduced states is easily controlled by the electrochemical method. The analysis provided evidence that the semiquinone radical plays a predominant role in the autoxidation. The generation of a superoxide anion radical as a product of the one-electron transfer from the semiquinone to O2 was confirmed by the reduction of ferricytochrome c. The fact that the catalytic reduction wave of O2 increases with pH was ascribed to the increase in the semiquinone formation constant. The mechanism of the reoxidation of reduced flavoprotein glucose oxidase with O2 was also examined. The result supports the semiquinone-dependent one-electron transfer as the mechanism.