Electrochemical reduction of methemoglobin either directly or with flavin mononucleotide as a mediator.

Electrochemical reduction of methemoglobin on a platinum electrode is studied by means of thin layer spectroelectrochemistry. For methemoglobin alone in solution, direct reduction is very slow even for potentials close to those of the reduction of the solvent. The reduction of a methemoglobin-oxyhemoglobin mixture with an imposed potential causes the electrochemical reduction of oxygen, the conversion of oxyhemoglobin into deoxyhemoglobin, and a simultaneous transformation of part of the molecules into methemoglobin. When fixed oxygen has disappeared, reduction of methemoglobin takes place. The reduction of methemoglobin and deoxyhemoglobin is catalyzed by the presence of flavin mononucleotide (FMN). For the oxyhemoglobin-methemoglobin mixture, flavin makes a fast deoxygenation of oxyhemoglobin without a change in the oxidation state of the iron. It also allows the rapid reduction of methemoglobin. In each case, the resulting deoxyhemoglobin solutions do not show any electrolysis-induced modification of the equilibrium curves for oxygen binding.