Ultrasonic absorption and relaxation spectra in aqueous bovine hemoglobin

Measurements of the frequency and pH dependence of acoustic absorption at 0°C in aqueous solutions of freshly prepared bovine oxyhemoglobin are reported. The role of ionization and possible direct proton‐transfer between proximal pairs in determining the characteristic times for the relaxation of the internal charge distribution is discussed. It is concluded that treatments which consider various classes of residues as ionizing independently will not give approximately correct relaxation spectra. A model which takes into account the coupling between the degrees of ionization of the various residues is found to give rough agreement with the observed acoustic absorption in the pH range in which the native conformation is stable.