MECHANISTIC STUDY OF THE AUTOXIDATION OF REDUCED FLAVIN AND QUINONE COMPOUNDS

The mechanism of the autoxidation of reduced flavin and quinone compou nds was investigated through semiquantitative analysis of voltammetric waves of the reduction of dioxygen (O-2) catalyzed by flavin and quin one adsorbed on electrode surfaces, where the redox equilibrium among the oxidized, (flavo)semiquinone and fully reduced states is easily co ntrolled by the electrochemical method. The analysis provided evidence that the semiquinone radical plays a predominant role in the autoxida tion. The generation of a superoxide anion radical as a product of the one-electron transfer from the semiquinone to O-2 was confirmed by th e reduction of ferricytochrome c. The fact that the catalytic reductio n wave of O-2 increases with pH was ascribed to the increase in the se miquinone formation constant. The mechanism of the reoxidation of redu ced flavoprotein glucose oxidase with O-2 was also examined. The resul t supports the semiquinone-dependent one-electron transfer as the mech anism. (C) 1998 Elsevier Science S.A. All rights reserved.