ELECTRON PARAMAGNETIC RESONANCE STUDIES OF NITRIC OXIDE HEMOGLOBIN DERIVATIVES .I. HUMAN HEMOGLOBIN SUBUNITS

To elucidate the molecular conformation of a ligand bound to hemoglobin, nitric oxide derivatives of human adult hemoglobin and its subunits (α and β) have been studied by electron paramagnetic resonance spectroscopy. The spectrum of hemoglobin α-NO and β-NO are dissimilar and that of erythrocytes NO and human adult hemoglobin NO are the arithmetic mean of the spectrum for the isolated subunits. At room temperatures, the signal of hemoglobin α-NO exhibits axial symmetry, whereas that of hemoglobin β-NO slightly deviates from axial symmetry. Below -50°, however, the signal for both the subunits markedly distorts from axial symmetry. The approximate principal g values have been estimated by comparing the observed spectra with simulated spectra calculated by a digital computer. For the simulation, a broad intrinsic line width had to be assumed, which may be due to a freedom of the orientation of NO on heme. Urea and high pH broaden the signal of hemoglobin β-NO. The effect of temperature and denaturing agents on the signal shape can be explained by the change of orientational freedom of liganded NO associated with the conformational change of globin moiety. © 1969, American Chemical Society. All rights reserved.