Reactions of aquacobalamin (HO-Cbl(III)) and its one-electron reduced form (cob(II)alamin, Cbl(II)) with chlorite (ClO) and chlorine dioxide (ClO ) were studied by conventional and stopped-flow UV-Vis spectroscopies and matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). ClO does not react with HO-Cbl(III), but oxidizes Cbl(II) to HO-Cbl(III) as a major product and corrin-modified species as minor products. The proposed mechanism of chlorite reduction involves formation of OCl that modifies the corrin ring during the course of reaction with Cbl(II). HO-Cbl(III) undergoes relatively slow destruction by ClO via transient formation of oxygenated species, whereas reaction between Cbl(II) and ClO proceeds extremely rapidly and leads to the oxidation of the Co(II)-center.
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