title: Reaction of nitric oxide with heme proteins: studies on metmyoglobin, opossum methemoglobin, and microperoxidase.
abstract: Kinetic and EPR studies show that the first step in the reaction of NO with ferric myoglobin, opossum hemoglobin, and microperoxidase is the reversible formation of the H-NO complex: H + NO in equilibrium H-NO (where H = Mb+, or Hb+ OP, or MP+). The NO-combination rates are markedly affected by the presence or absence of the distal histidine. The distal histidine significantly reduces the NO-combination rates, perhaps by interaction between the distal histidine and the ferric iron. Thus the beta-chains of Hb+ OP and metmyoglobin show similar combination rates. In the absence of a distal histidine, the NO-combination rates in the alpha-chains of Hb+ OP are much faster and similar to those observed for the five-coordinate heme in microperoxidase. The loss of a water molecule from the six-coordination site is assumed to be the rate-limiting step.
mesh_terms: D000818:Animals; D004578:Electron Spin Resonance Spectroscopy; D006420:Hemeproteins / Q000378:metabolism*; D007700:Kinetics; D008706:Methemoglobin / Q000378:metabolism; D008786:Metmyoglobin / Q000378:metabolism; D009569:Nitric Oxide / Q000097:blood*; D009893:Opossums; D010544:Peroxidases / Q000378:metabolism*; D013053:Spectrophotometry
chemical_list: D006420:Hemeproteins; D008786:Metmyoglobin; D009569:Nitric Oxide; D008706:Methemoglobin; D010544:Peroxidases; C021799:microperoxidase