Kinetic studies on the reaction of cob(II)alamin with hypochlorous acid: Evidence for one electron oxidation of the metal center and corrin ring destruction

Kinetic and mechanistic studies on the reaction of a major intracellular vitamin B12 form, cob(II)alamin (Cbl(II)), with hypochlorous acid/hypochlorite (HOCl/OCl−) have been carried out. Cbl(II) (Co(II)) is rapidly oxidized by HOCl to predominately aquacobalamin/hydroxycobalamin (Cbl(III), Co(III)) with a second-order rate constant of 2.4×107M−1s−1 (25.0°C). The stoichiometry of the reaction is 1:1. UHPLC/HRMS analysis of the product mixture of the reaction of Cbl(II) with 0.9mol equiv. HOCl provides support for HOCl being initially reduced to Cl and subsequent H atom abstraction from the corrin macrocycle occurring, resulting in small amounts of corrinoid species with two or four H atoms fewer than the parent cobalamin. Upon the addition of excess (H)OCl further slower reactions are observed. Finally, SDS-PAGE experiments show that HOCl-induced damage to bovine serum albumin does not occur in the presence of Cbl(II), providing support for Cbl(II) being an efficient HOCl trapping agent. Kinetic and mechanistic studies on the reaction between cob(II)alamin (Cbl(II)) and hypochlorous acid have been carried out. The reaction is extremely rapid (2.4×107M−1s−1) and H atom abstraction from the corrin ring occurs. [Display omitted] •Products analyzed by Ultra High Performance Liquid Chromatography/High Resolution Mass Spectrometry (UHPLC/HRMS).•(H)OCl rapidly oxidizes the metal center of cob(II)alamin (Cbl(II)) with a 1:1 Cbl(II):HOCl stoichiometry.•HOCl is reduced to Cl and corrinoid products are formed with two or four fewer H atoms than the parent molecule.•HOCl-induced damage to bovine serum albumin does not occur in the presence of Cbl(II).