Copper and oxidation of hemoglobin: a comparison of horse and human hemoglobins

Abstract

Oxidation studies of hemoglobin by Cu(II) indicate that for horse hemoglobin, up to a Cu(II)/heme molar ratio of 0.5, all of the Cu(II) added is used to rapidly oxidize the heme. On the other hand, most of the Cu(II) added to human hemoglobin at low Cu(II)/heme molar ratios is unable to oxidize the heme. Only at Cu(II)/heme molar ratios greater than 0.5 does the amount of oxidation per added Cu(II) approach that of horse hemoglobin. At the same time, binding studies indicate that human hemoglobin has an additional binding site involving one copper for every two hemes, which has a higher copper affinity than the single horse hemoglobin binding site. The Cu(II) oxidation of human hemoglobin is explained utilizing this additional binding site by a mechanism where a transfer of electrons cannot occur between the heme and the Cu(II) bound to the high affinity human binding site. The electron transfer must involve the Cu(II) bound to the lower affinity human hemoglobin binding site, which is similar to the only horse hemoglobin site. The involvement of beta-2 histidine in the binding of this additional copper is indicated by a comparison of the amino acid sequences of various hemoglobins which possess the additional site, with the amino acid sequences of hemoglobins which do not possess the additional site. Zn(II), Hg(II), and N-ethylmaleimide (NEM) are found to decrease the Cu(II) oxidation of hemoglobin. The sulfhydryl reagents, Hg(II) and NEM, produce a very dramatic decrease in the rate of oxidation, which can only be explained by an effect on the rate for the actual transfer of electrons between the Cu(II) and the Fe(II). The effect of Zn(II) is much smaller and can, for the most part, be explained by the increased oxygen affinity, which affects the ligand dissociation process that must precede the electron transfer process.

The oxidative effect of bacterial lipopolysaccharide on native and cross‐linked human hemoglobin as a function of the structure of the lipopolysaccharide

“…The rate of auto‐oxidation of cross‐linked Hb was greater than that of Hb A 0, both in the presence and absence of EDTA, as has been observed previously [17]. In addition, the rates of auto‐oxidation of both cross‐linked Hb and Hb A 0 were markedly reduced by EDTA, suggesting catalysis of the oxidation by heavy metal cations, as previously observed by Rifkind [8,18]. To determine whether the heavy metal cation was cupric ion as indicated by the results of Rifkind [8], the effect of a chelator specific for cupric ion, neocuproine [19,20], was studied.…”

Electron transfer and autoxidation kinetics of the bis(imidazole)bis(dimethylglyoximato)iron(II) complex

“…It is interesting to compare the mechanism proposed here for the copper catalyzed autoxidation of the [Fe(Hdmg)2(Him)2] complex with those previously reported for metalloproteins such as the cytochrome-c (6)(7)(8). In the case of the metalloproteins, the rate-determining step is the one electron oxidation of the biomolecule by the copper(I1) species.…”

“…In this work we have studied the properties and reactivity of the [Fe(Hdmg)2(Him)2] complex, with particular emphasis o n the electrochemistry and redox kinetics in aqueous solution. We have also investigated the autoxidation mechanisms, including the copper-catalyzed reaction, because of their possible relevance to the understanding of the biological oxidation processes (6)(7)(8). Experimental The electronic spectra of the complexes in the visible and uv region were recorded on a Cary 17 or a Hewlett-Packard 8451 diode-may spectrophotometer fittedwith thermostatted cell compartments.…”

Internal Electron Transfer between Hemes and Cu(II) Bound at Cysteine β93 Promotes Methemoglobin Reduction by Carbon Monoxide

“…Hb with only the ␤ chain hemes oxidized was prepared by addition of a 5-fold excess of CuSO 4 over oxyHb. It has been shown (2,16,17) that under these conditions the ␤ chain hemes are selectively oxidized, whereas the ␣ chain hemes remain in the reduced, ferrous state.…”