Issue 8, 1989

Electron transfer between α and β haem groups in haemoglobin. An electron spin resonance study

Abstract

We have previously shown that when haemoglobin hybrids containing FeIII and (FeO2) units are exposed to 60Co γ-rays, ejected electrons add in a highly specific manner to both units, addition to the (FeO2) units being preferred. This suggested that intramolecular electron transfer from the unstable (FeO2) centres to FeIII to give the stable FeII form is immeasurably slow in the 77–150 K range. [We cannot use higher temperatures because the (FeO2) units change, probably as a result of protonation to give Fe—O2H units.] This result was unexpected in view of the relatively fast reactions occurring over similar distances in proteins, including haemoglobin hybrids. One possible error in our argument lies in the cooperative effect of oxygen binding which could negate the results, since the transfer considered is clearly impossible within (FeO2)3(FeO2) molecules. Thus, even if the transfer within hybrid units were rapid, (FeO2) centres would remain unchanged in (FeO2)3(FeO2) molecules, and it could have been these (FeO2) units that were studied, those formed in hybrids having undergone electron transfer so rapidly that they were lost prior to e.s.r. studies.

Working at low concentrations of (FeO2), we have established that reaction to give (FeO2) remains favourable and that the units remain stable. The results rule out the possibility of fast electron transfer . As a further check, we have studied the stability of (FeO2) units in the mutant haemoglobin M Iwate. The form used, (a2Mmet β2oxy) has all its α chains fixed as FeIII, whereas the β-chains take up oxygen normally to give oxyhaem units. Again, electron capture on irradiation was favoured at the (FeO2) units, and, at low doses, these must be in molecules containing at least one FeIII units. The (FeO2) centres were stable in the 77–150 K region, having e.s.r. properties closely similar to those in the β-chains of normal oxyhaemoglobin.

We conclude that electrons are not transferred from (FeO2) to FeIII at low temperatures when the (FeO2) unit is in the β-chains and FeIII is in the α-chains.

Article information

Article type
Paper

J. Chem. Soc., Faraday Trans. 1, 1989,85, 2427-2433

Electron transfer between α and β haem groups in haemoglobin. An electron spin resonance study

M. C. R. Symons and F. A. Taiwo, J. Chem. Soc., Faraday Trans. 1, 1989, 85, 2427 DOI: 10.1039/F19898502427

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