Kinetics of cobinamide (Cbi) reduction by glucose and fructose was studied at alkaline solutions. It was shown that the reaction of cobinamide with monosaccharides leads to the formation of Co(I) complex in contrast to the reduction of aquacobalamin (H 2 OCbl) resulting in the formation of Cbl(II).

Glutathionylcobalamin (GSCbl), a tight complex of glutathione (GSH) with cobalamin(III), is readily oxidized to aquacobalamin by hypochlorite. Corrin macrocycle remains unmodified in the presence of threefold excess of hypochlorite, whereas aqua- and cyanocobalamins are partially transformed to chlorinated species under the same conditions. The suggested mechanism of reaction between GSCbl and hypochlorite involves subsequent oxidation of thiol and amino groups and dissociation of oxidized glutathione from Co(III)-ion.

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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