Efficient Trapping of HNO by Deoxymyoglobin

Abstract

Nitrosyl hydride, HNO, also commonly termed nitroxyl, is a transient species that has been implicated in the biological activity of nitric oxide, NO. Herein, we report the first generation of a stable HNO-metal complex by direct trapping of free HNO. Deoxymyoglobin (Mb-Fe(II)) rapidly reacts with HNO produced from the decomposition of methylsulfonylhydroxylamine (MSHA) or Angeli's salt (AS) in aqueous solutions from pH 7 to pH 10, forming an adduct, Mb-HNO. The unique 1H NMR signal of the Fe-bound HNO at 14.8 ppm allows definitive proof of its formation. The generation of Mb-HNO and quantification of various myoglobin byproducts were accomplished by correlation of 1H NMR, UV-vis, and EPR spectroscopies. Typically, the maximum Mb-HNO yield obtained is 60-80%; competitive side reactions with byproducts as well as the further reactivity of the Mb-HNO decrease the overall yield. At pH 10, the observed rate of Mb-HNO generation by trapping HNO from MSHA is close to that for MSHA decomposition; kinetic simulations give a lower limit to the bimolecular rate of trapping as 1.4 x 10(4) M(-1) s(-1). The binding of HNO to deoxymyoglobin is rapid and essentially irreversible, which suggests that the biological activity of nitroxyl may be mediated by its reactivity with ferrous heme proteins such as myoglobin and hemoglobin.

Oxygen-regulated isoforms of cytochrome c oxidase have differential effects on its nitric oxide production and on hypoxic signaling

“…This group includes hemoglobin and myoglobin (43)(44)(45)(46)(47). The rate of NO production by Cco increases with decreasing pH and increasing NO 2 Ϫ concentration (21), suggesting that that Cco functions in a nitrite reductase reaction (NO 2 Ϫ ϩ FeII ϩ H ϩ 3 NO ϩ FeIII ϩ OH Ϫ ) similar to that proposed for hemoglobin and myoglobin (48)(49)(50)(51)(52). Unlike the Cco oxidase reaction, which requires four electrons, the Cco NO 2 Ϫ reductase reaction involves a one-electron transfer.…”

The Interaction of Nitric Oxide with Distinct Hemoglobins Differentially Amplifies Endothelial Heme Uptake and Heme Oxygenase-1 Expression

“…Both the NO ϩ and NO Ϫ donors used have been shown to undergo conversion to NO under comparable conditions; GSNO is converted to NO by Cu (Singh et al, 1996) or heme (Spencer et al, 2000), and nitroxyl (AS) is oxidized to NO by reaction with oxygen (Han et al, 2002). There are also several fundamental reactions possible between the different states of Hb and NO or nitroxyl (Pawloski et al, 2001;Sulc et al, 2004) (Table 1). It is important to note that the final products are typically the same: the ferrous nitrosyl, NO-Hb, results from reactions of NO x donors with deoxy or metHb, whereas for oxyHb reactions with NO x generally yield the oxidized metHb.…”

The Chemistry and Biology of Nitroxyl (HNO): A Chemically Unique Species with Novel and Important Biological Activity

“…[78] The analogous hemoglobin complex has also been formed by reacting HNO directly with deoxyhemoglobin. [79] Thus, other possible biological targets for HNO are the metal centers of metalloproteins: HNO can reduce oxidized metal centers, possibly followed by complexation of NO to form the metal nitrosyl [Eq. (15)], or directly bind reduced metal centers as HNO.…”