Reactions of persulfides with the heme cofactor of oxidized myoglobin and microperoxidase 11: reduction or coordination.

Persulfides of cysteine (CysSSH), glutathione (GSSH) or N-methoxycarbonyl-penicillamine (NAcPenSSH) react with the ferric form of myoglobin (metMb(III)) to yield the oxy-ferrous (oxyMb(II)) or deoxy-ferrous (deoxyMb(II)) forms of myoglobin under aerobic or anaerobic conditions, respectively. Under aerobic conditions, CysSSH and NAcPenSSH react with the hypervalent form of myoglobin (ferrylMb(IV)) to yield oxyMb(II) as the final product with the formation of metMb(III) as an intermediate. CysSSH and NAcPenSSH coordinate the ferric form of N-acetylated microperoxidase (NAcMP11(III)) to yield the disulfanido complex NAcMP11(III)(NAcPenSS), as shown by UV-vis and EPR spectroscopy. Experiments carried out with various NAcMP11 derivatives demonstrate a redox equilibrium between the ferric/ferrous forms of the heme and the polysulfides/persulfides couple. Our results suggest that persulfides possess uncommon redox properties, analogous to that of dihydrolipoic acid.