CIRCULAR DICHROISM OF ISOLATED AND RECOMBINED HEMOGLOBIN CHAINS

The optical activity of the heme bands of hemoglobin has been used as a probe to study the alterations of the structure of the isolated α and β chains on recombination to form the normal tetrameric molecule. In all oxidation and ligand states, the circular dichroism spectra of the two chains differ both in the Soret and in the visible region and are readily distinguishable from each other by this technique. The circular dichroism bands exhibit distinctive peak positions, molar ellipticities, and rotational strengths, reflecting a difference in the environments of the heme in the α from that of the β chains. Chain recombination induces a circular dichroism spectrum identical with that of native hemoglobin, but different from that of the noninteracting mixture, indicating an alteration of the heme environments upon recombination. The largest variations are observed upon recombination of the deoxy chains. Chain recombination when studied in the region of absorption of the peptide chromophore does not appear to indicate a change in the conformation of the molecule except in the case of the deoxy derivative, where there is an increase in the depth of the 233-nm Cotton effect trough comparable with that observed upon deoxygenation of hemoglobin. © 1969, American Chemical Society. All rights reserved.