Regulation of vascular tone by S-nitroso-myoglobin

Myoglobin (Mb) is a haem protein present in skeletal, cardiac and smooth muscle where it facilitates the transfer of O(2) from the extracellular matrix to the cell cytosol in a cycle termed 'facilitated O(2)-diffusion'. In addition, we showed recently that recombinant human Mb binds endothelium-derived relaxant factor - nitric oxide ((.-)NO) - via formation of both nitrosyl-haem iron and S-nitroso-myoglobin (S-NO-Mb). S-NO-Mb represents a novel form of endothelium-derived relaxant factor (EDRF) that may be important in maintaining optimal (.-)NO concentrations in the human vasculature. In this study we aim to show that: (i) S-nitrosation of oxygenated ferrous myoglobin (oxyMb) can compete with the rapid oxidation of (.-)NO by oxyMb; and (ii) S-NO-Mb retains characteristics of physiological EDRF.