Non-equilibrium state of a monomeric insect haemoglobin induced by γ-irradiation and detected by Mössbauer spectroscopy

AbstractThe met-aquo form of the monomeric insect haemoglobin CTT III has been investigated by Mössbauer spectroscopy before and after reduction with thermolyzed electrons at low temperature. The native met haemoglobin dissolved in water and water/glycerol mixtures, respectively, exhibits in the range of pH 5.8 to 9.0 high-spin iron(III). The electronic state of the haemoglobin is not affected by the solvent conditions. In water/glycerol γ-irradiation at 77 K results in the reduction of the haem iron by thermolyzed electrons. Due to this process, the hexacoordinated high-spin iron(III) is transformed into a hexacoordinated low-spin iron(II). This latter complex is a transition state which changes into the high-spin iron(II) state of the deoxyhaemoglobin when increasing the temperature. Thus, a kinetically stabilized non-equilibrium state of the haemoglobin exists at low temperature which relaxes with increasing temperature and finally reaches the equilibrium state to form deoxyhaemoglobin. This transition occurs at T > 190 K and corresponds with drastic changes in the temperature dependence of the Lamb-Mössbauer factor. Both effects indicate an alteration of the intramolecular flexibility of the haemoglobin