Implication of the alpha 1 beta 1 interface in the hemoglobin affinity changes. A comparative study between normal and San Diego fully ligated hemoglobins.

The alpha 1 beta 1 interface of normal and mutated San Diego hemoglobins in their fully liganded form was investigated, through the SH vibrational absorption of beta-112 cysteine, by Fourier-transform infrared spectroscopy. The center frequency of this thiol group was significantly shifted in San Diego hemoglobin compared with normal human hemoglobin. Different dimer organization between the two proteins was also revealed by circular dichroism of the heme. These findings agree well with assessment that the alpha 1 beta 1 interface, far from being inert, is involved in the affinity changes of the hemoglobin molecule.