Soret circular dichroism of cobalt-substituted myoglobin and hemoglobin derivatives

Abstract

Circular dichroic spectra in the Soret region were obtained for the following cobalt-substituted hemoproteins: CoMb ‡ ‡ Abbreviations used: Mb, myoglobin; Hb, hemoglobin; FeHbO 2, native oxyhemoglobin; CoHbO 2, cobalto-oxyhemoglobin; FeHb, native deoxyhemoglobin; CoHb, cobaltodeoxyhemoglobin; FeHb +, native ferrihemoglobin; CoHb +, cobaltihemoglobin; CoHbNO, nitrosylcobaltohemoglobin; FeHbNO, native nitrosylhemoglobin (similar abbreviations were used for myoglobin derivatives); c.d., circular dichroism; IHP, inositol hexaphosphate. , CoMbO 2, CoMbNO, CoMb +, CoHb, CoHbO 2, CoHbNO and CoHb + and compared with the corresponding spectra of the native species to delineate the sensitivity of Soret circular dichroism to ligation, quaternary structures, metal ion substitution and its magnetic moment. Soret rotational strengths, R, were calculated, and dissymmetry ratios were used to reveal hidden transitions. The results indicate that Soret circular dichroism is sensitive to the metal ion, its oxidation state, ligation and local environment but neither to quaternary structural changes as proposed by Ferrone & Topp (1975), nor to the magnetic moment of the metal ion as suggested by Li & Johnson (1969).