Formation of Nitric Oxide Myoglobin: Mechanisms of the Reaction with Various Reductants

Abstract

SUMMARY– The concentration, temperature and pH dependences of the formation of nitric oxide myoglobin (NOMb) from metmyoglobin nitrite (MetMb·NO 2 ) were determined for nitrite and the reductants, ascorbic acid, cysteine, hydro‐quinone, nicotinamide adenine dinucleotide (NADH) and glyceraldehyde. The reaction for all reductants except glyceraldehyde involves the production of a nitroso‐reductant intermediate which breaks down to release nitric oxide. The latter forms a nitric oxide metheme complex (Fe +++ ) which is then reduced to the ferrous state (Fe ++ ). With cysteine and NADH there is a second pathway which probably involves the direct reduction of MetMb NO 2 . Ascorbate and hydro‐quinone form nitroso intermediates that are stabilized in alkali. The effects of oxygen, ethylenediaminetetraacetic acid and cytochrome c on the reaction were determined. Oxygen slows or inhibits the reaction, while the latter two have no effect on the reaction as studied.