George H. Bare

Fourier transform infrared spectroscopic study of molecular interactions in hemoglobin

Infrared absorption spectra of the alpha-104 (G11) cysteine SH group have been observed for aqueous solutions of hemoglobin derivatives from humans, pigs, and horses. The center frequencies ((nu)SH) show ligand sensitive patterns that are similar for the three species, with (nu)SH (HbCO) <(nu)SH (HbO(2) ~ HbCN) < (nu)SH (Hb(+)) <<(nu)SH (deoxyHb) for human and pig hemoglobins. The alpha-104 SH group is most strongly H-bonded (smallest (nu)SH), has the greatest range of (nu)SH (Hb ? HbCO) in human hemoglobin, and is least strongly H-bonded and has the smallest range of (nu)SH (Hb ? HbCO) in horse hemoglobin. The beta-112 cysteine SH in human hemoglobin is more weakly H-bonded than is the alpha-104 SH. These studies illustrate how FTIR can be used to measure differences in protein structure that are related to biological control mechanisms.

FOURIER TRANSFORM INFRARED SPECTROSCOPY OF HEMOGLOBIN1

Fourier transform infrared spectroscopy has become a powerful probe of local molecular structure in biological macromolecules. Vibrational absorption bands from each of the cysteine SH groups in hemoglobin have been identified and studied by use of aqueous solutions of human, pig, horse, and cow hemoglobin, and isolated α-chains. The vibrational absorption band frequency of α-104 cysteine SH is highly sensitive to change in α-chain tertiary structure and quaternary structure of the tetramer, and is modulated by the heme-ligand complex in the sequence, HbCO 2 ˜ HbCN) + −1 and 1107 cm −1 by Fermi resonance with the iron-oxygen vibrational overtone. This strong vibrational coupling is associated with a polarized covalent iron-oxygen bond.

Heme-protein structural interactions in hemoglobin studied by fourier transform infrared spectroscopy.

Fourier transform infrared spectroscopy provides the sensitivity, selectivity, and variety of absorptions required for a probe of molecular structure in biological systems. We have developed these spectroscopic methods and applied them to the study of interactions between heme and protein that permit biological control of oxygen transport in hemoglobin. Several absorptions have been identified with specific group vibrations which act as structural probes of known locations within the molecule. The best studied of these are ligands coordinated to the heme iron, and the cysteine sulfhydryl groups which may be studied individually because of their different local surroundings.