Reaction of human myoglobin and nitric oxide. Heme iron or protein sulfhydryl (s) nitrosation dependence on the absence or presence of oxygen.

The amino acid sequence of human myoglobin (Mb) is similar to other mammalian Mb except for a unique cysteine residue at position 110 (Cys(110)). Anaerobic treatment of ferrous forms of wild-type human Mb, the C110A variant of human Mb or horse heart Mb, with either authentic NO or chemically derived NO in vitro yields heme-NO complexes as detected by electron paramagnetic resonance spectroscopy (EPR). By contrast, no EPR-detectable heme-NO complex was observed from the aerobic reactions of NO and either the ferric or oxy-Mb forms of wild-type human or horse heart myoglobins. Mass analyses of wild-type human Mb treated aerobically with NO indicated a mass increase of approximately 30 atomic mass units (i.e., NO/Mb = 1 mol/mol). Mass analyses of the corresponding apoprotein after heme removal showed that NO was associated with the apoprotein fraction. New electronic maxima were detected at A(333 nm) (epsilon = 3665 +/- 90 mol(-)(1) cm(-)(1); mean +/- S.D.) and A(545 nm) (epsilon = 44 +/- 3 mol(-)(1) cm(-)(1)) in solutions of S-nitrosated wild-type human Mb (similar to S-nitrosoglutathione). Importantly, the sulfhydryl S-H stretch vibration for Cys(110) measured by Fourier transform infrared (nu approximately 2552 cm(-)(1)) was absent for both holo- and apo- forms of the wild-type human protein after aerobic treatment of the protein with NO. Together, these data indicate that the reaction of wild-type human Mb and NO yields either heme-NO or a novel S-nitrosated protein dependent on the oxidation state of the heme iron and the presence or absence of dioxygen.