Circular Dichroism Spectra of Hemoglobins

This chapter deals with the circular dichroism (CD) spectra of hemoglobins. The measurement of CD spectra as a tool to investigate the structural organization of protein molecules is of particular advantage for hemoglobins. These molecules contain, in addition to the protein moiety, the heme, with electronic transitions that are quite intense, diverse, and very sensitive both to the surrounding environment and to ligand binding. This situation offers three distinct regions of investigation, each containing information concerning a part of the structural organization of the hemoglobin molecule. Consequently, the optical activity of hemoglobin spectra depends on the relative positions of the different chromophores in the tridimensional organization of the molecule. Alterations of the relative positions in different conformational states are likely to cause alterations in the interactions from which the CD spectra of the different chromophores derive. This is the reason that CD is so sensitive to the conformational states of the molecule. The chapter also presents the informational content of CD spectra.