Ultrasonic Examination of the Hemoglobin Dissociation Process in Aqueous Solutions of Guanidine Hydrochloride

The ultrasonic absorption was determined, in aqueous solutions of hemoglobin undergoing dissociation as a function of the strong electrolyte guanidine hydrochloride (GuHCl), up to 5.4M (molar), over the frequency range 1–50 MHz. With increasing GuHCl concentration to 0.7M, the Hb molecule dissociates into half-molecules without loss of tertiary structure, and at GuHCl concentrations greater than 2.5M, the Hb molecule dissociates further into its four individual polypeptide chains with complete loss of tertiary structure. The ultrasonic absorption coefficient appears to be insensitive to the dissociation process, though a small contribution appears at the lower frequencies, owing to the expansion of the polypeptide molecule. A maximum in the absorption occurs near 2M GuHCl concentration, which does not correspond to dissociation or expansion of the Hb molecule, and it is thought to be associated with the proton transfer reaction.