Nature of the negative ellipticity of human fetal hemoglobin in the 280 nm region

The uv circular dichroism (CD) spectra of aquomet hemoglobins A and F were followed to monitor their R→T conformational change. Titration studies with inositol hexaphosphate (IHP) for both adult and fetal hemoglobin showed identical total ellipticity changes although HbF was found to possess an inherently negative ultraviolet CD spectrum. By monitoring changes in the protein portion of the molecule, a dissociation constant for IHP of 16 μM was obtained for HbF. Chemical modification of HbF was found to leave the negative ellipticity unperturbed relative to native HbF. The results suggest that the negative ellipticity seen for stripped aquomet HbF is not due to a T conformation, but rather to an amino acid substitution in the γ chain of HbF.