1H electron-nuclear double resonance of cobalt hemoglobin.

Proton 1H electron-nuclear double resonance spectra were obtained from cobalt-substituted hemoglobin A. For oxy cobalt-substituted hemoglobin (CoHb), two major couplings were found. One is exchangeable by deuterium and has a coupling of approximately 5.6 MHz which is assigned to the N epsilon 2-proton of the distal histidine (E7), interacting with the ligand. The other splitting (approximately 2.4-3.2 MHz) is attributed to a methyl-proton on Val (E11). No coupling of protons on the proximal side is resolved. Deoxy CoHb exhibits only one prominent interaction (approximately 1.3 MHz) which is assigned to one of the protons on the proximal histidine (F8). The influence of the distal amino acids His (E7) and Val (E11) on the ligand affinity in oxy CoHb is discussed.