Redox mechanism of lumazine at a glassy carbon electrode

The electrochemical behaviour of lumazine, a pterin compound which acts as substrate for the lumazine synthase/riboflavin synthase complex, has been studied at a glassy carbon electrode using cyclic, differential pulse and square wave voltammetry. The oxidation of lumazine was possible only in electrolytes with pH > 7.0 since it occurred at very high potential values. It is an irreversible, pH-dependent process that occurred with the transfer of two electrons and two protons and did not involve the formation of any electroactive oxidation product. The reduction of lumazine was studied over a wide pH range and occurred with the transfer of two electrons and two protons. In acid electrolytes the reduction was quasi-reversible and occurred with the formation of several reduction products that were oxidized at the glassy carbon surface and for higher pH the reduction became reversible. The diffusion coefficient of lumazine was calculated in pH 7.0 0.1 M phosphate buffer to be DLMZ = 9.1 × 10−6 cm2 s−1. The electroanalytical determination of lumazine was carried out in pH 7.0 0.1 M phosphate buffer using differential pulse voltammetry with a detection limit LOD = 0.76 μM. A mechanism for both oxidation and reduction of lumazine is proposed.