The rate of reaction of superoxide radical ion with oxyhaemoglobin and methaemoglobin

Abstract

Superoxide radical ions (O2-) produced by the radiolytic reduction of oxygenated formate solutions and by the xanthine oxidase-catalysed oxidation of xanthine were shown to oxidize the haem groups in oxyhaemoglobin and reduce those in methaemoglobin as in reactions (1) and (2): (see articles) Reaction (1) is suppressed by reaction (8) when [O2-]exceeds 10 muM, but consumes all the O2- generated in oxyhaemoglobin solutions when [oxyhaemoglobin] greater than 160 muM and [O2-]less than 1 nM at pH 7. The yield of reaction (2) is also maximal in methaemoglobin solutions under similar conditions, but less than one haem group is reduced per O2- radical. From studies of (a) the yield of reactions (1) and (2) at variable [haemoglobin] and rates of production of O2-, (b) their suppression by superoxide dismutase, and (c) equilibria observed with mixtures of oxyhaemoglobin and methaemoglobin, it is shown that k1/k2=0.7 +/- 0.2 and k1 = (4 +/- 1) X 10(3) M-1-S-1 At pH7, and k1 and k2 decrease with increasing pH. Concentrations and rate constants are expressed in terms of haem-group concentrations. Concentrations of superoxide dismutase observed in normal erythrocytes are sufficient to suppress reactions (1) and (2), and hence prevent the formation of excessive methaemoglobin.

Metabolism of Pyrogallol to Purpurogallin by Human Erythrocytic Hemoglobin

“…A plausible mechanism for the oxidation of oxyhemoglobin by pyrogallol may be proposed as the process shown in Scheme 1. Namely, oxyhemoglobin will be oxidized by pyrogallol to ferric form producing hydrogen peroxide (H 2 O 2 ) as has been suggested for the mechanism of oxyhemoglobin oxidation by some reductants such as phenol and hydroquinone by Wallace and (Eyer et al 1975;Sutton et al 1976). Therefore, the oxidation rate of oxyhemoglobin will be suppressed by scavenging these active oxygens in the presence of superoxide dismutase and catalase.…”

Up-regulation of α1-microglobulin by hemoglobin and reactive oxygen species in hepatoma and blood cell lines

“…The auto-oxidation of oxyhemoglobin and downstream free-radical formation is largely prevented by the intracellular inhibitors superoxide dismutase, catalase, and glutathione peroxidase [4,5]. In spite of this, slow auto-oxidation occurs intracellularly.…”

Effects of heme proteins on nitric oxide levels and cell viability in isolated PMNs: a mechanism of toxicity

“…Internalized heme proteins could also interact with O 2 ·Ϫ produced by PMN vacuoles. Because the reaction of O 2 ·Ϫ with NO · to form ONOO Ϫ is extremely rapid (3.7 ϫ 10 7 M -1 · s -1 ) [22], it is conceivable that heme proteins (3-30 µg/mL) bound to plasma or vacuole membranes bind and/or dismute O 2 ·Ϫ , thereby increasing the NO · concentration by limiting the scavenging action of O 2 ·Ϫ . This model is consistent with other reported data showing that PMNs activated with the PMA concentration used in this investigation produced twice the number of moles of O 2 ·Ϫ as NO · [21] and that low concentrations of SOD increase NO · levels [18,49,50].…”

“…The levels of O 2 ·Ϫ produced by PMA-activated PMNs have been reported to exceed NO · levels by twofold [21]. Superoxide reacts rapidly with NO · to form peroxynitrite (ONOO Ϫ ), with rates of 37 ϫ 10 6 · M -1 · s -1 [22] and more slowly with both oxyHb and metHb to form metHb and oxyHb and H 2 O 2 and O 2 , respectively [23]. Peroxynitrite is a larger, charged compound that should not enter neighboring cells as readily as NO · .…”