Rates of release of nitric oxide from HbSNO and internal electron transfer.
The discovery that hemoglobin (Hb) in erythrocytes contains a fraction of beta-Cys-93 thiols as the nitrosylated derivative (HbSNO) led to the suggestion that this species is involved in transporting and releasing nitric oxide, which is the signal for local vasodilation. The release of NO from HbSNO requires an electron transfer to facilitate release and to regenerate the cysteine thiol via one-electron reduction in the absence of added thiols. An alternative mechanism, which has received much attention, transfers the nitrosyl group to an external thiol, which in turn would have to be reduced. The observed first order rate constant for the spontaneous oxidation of the ferrous heme of deoxy HbSNO is 1.0 x 10(-4)s(-1) in the absence of thiols. Under the same conditions, native Hb is stable. The oxidation of HbSNO occurs with the same rate constant that can be derived for the rate reported for the formation of HbNO from HbSNO. These similarities suggest that both processes involve the same reaction: internal electron transfer and direct release of nitric oxide.
Ship
Noam J
NJ
Department of Chemistry, Davenport Chemistry Research Building, University of Toronto, Toronto, ON, Canada M5S 3H6.
Pezacki
John Paul
JP
Kluger
Ronald
R
D004579:Electron Transport; D006454:Hemoglobins / Q000737:chemistry*; D008706:Methemoglobin / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry*; D009603:Nitroso Compounds / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry*
D006454:Hemoglobins; D009603:Nitroso Compounds; C008657:nitrosyl hemoglobin; D009569:Nitric Oxide; D013455:Sulfur; D008706:Methemoglobin