The NO-mediated Reduction of FerrylMb and FerrylHb

It has been proposed that the highly oxidizing species ferrylMb is, at least in part, responsible for the oxidative damage caused by the reperfusion of ischemic tissues. We have determined the rate constants for the reactions of ferrylMb and ferrylHb with NO ((17.1 0.3) x 106 m-1 s-1 and (24 + 1) x 106 m-1 s-1 at pH 7.0 and 20 °C) [23, 24]. The large value of these rate constants implies that these reactions are very likely to occur in vivo and might represent a detoxifying pathway for ferrylMb and ferrylHb and, thus, an additional antioxidant function of NO.  

Local nitrite concentrations in tissues are linked to the amounts of NO produced. Indeed, except for nitrate generated from the reaction of NO with oxyHb, nitrite is the major end product of NO metabolism. Increased nitrite levels are thus found under pathophysiological conditions, for example inflammation, when N O production is elevated. We have found that the rate constants for the reactions of the ferryl forms of Mb and Hb with nitrite are significantly lower than those for the corresponding reaction with NO (16 + 1 m 1 s 1 at pH 7.5 for Mb and (7.5 + 0.1) x 102 m 1 s 1 at pH 7.0 for Hb, at 20 °C) [19, 20]. Thus, the reaction with nitrite probably plays a role only when NO has been consumed completely and large concentrations of nitrite are still present. 

---