Spectroscopic Investigation of Nitric Oxide-Cobalamin Interactions: Oxidation, Binding, and Biological Implications

Abstract This study explores the interactions between nitric oxide (NO) and cobalamin species, including hydroxocobalamin (B12a) and reduced cobalamin (B12), using absorption and electron paramagnetic resonance (EPR) spectroscopy. Key findings reveal that NO induces significant spectral changes in Cb(III), oxidizes Cb(II) to Cb(III), and forms a novel, reversible EPR-active adduct indicative of NO ligation to Cb(III). Additionally, porcine aortic endothelial cells partially reduce Cb(III) and release a superoxide cobalt(III) complex, with residual Cb(II) remaining cell-associated. These results suggest that cobalamin species modulate intracellular and tissue NO levels through redox reactions and reversible binding. The study also identifies a secondary reaction pathway involving NO, hydroxocobalamin, sodium hydroxide, and nitrogen dioxide, yielding sodium sulfate, sodium polysulfide, and sulfur dioxide as byproducts. These insights advance understanding of NO-cobalamin redox chemistry and its potential implications for NO regulation in biological systems through Ionic-channel research.