Assigment of heme and distal amino acid resonances in the proton NMR spectra of the oxyen and carbon monoxide complexes of soybean leghemoglobin

The 400 MHz ¹H-NMR spectra of the O₂ and CO complexes of ferrous soybean leghamoglobin α are reported. Spain decoupling and proton-proton nuclear Overhauser effect experiments have allowed specific assignment of the resonances of all of the heme substituent groups except the propionic acid side-chains. The resonances of the side chains of the important distal amino acids, Ph-44, His-61 and Leu-65, and the C-4 proton of the proximal histidine (His-92) have also been assigned. The NMR spectra indicate substantial conformational differences near the heme in oxy- and carbonmonoxyleghemoglobin. There appear to be no significant differences in the iron-proximal histidine distance.