Conformational equilibria in spin-labeled hemoglobin

A component characteristic of deoxyhemoglobin appears in the paramagnetic resonance spectrum of spin-labeled oxyhemoglobin, and vice versa, under conditions of pH and ionic strength consistent with the interpretation that the spectrum is sensitive to the conformational equilibrium of the carboxy-terminal histidines. The oxygenation-induced change in the resonance spectrum is discussed in terms of shifts in this equilibrium.