Ultrasonic absorption of bovine serum albumin solutions in the frequency range 60 to 160 kHz

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Abstract
The ultrasonic absorption of the globular protein bovine serum albumin in aqueous solution has been measured in the frequency range 60 to 160 kHz using a 2-1 spherical resonator. The effect of pH change and of the denaturants urea, guanidine hydrochloride, and sodium dodecyl sulfate on the absorption loss has been studied. It is concluded that a significant ultrasonic absorption process exists which is related to structural helix-coil transition equilibria. For native protein the maximum loss appears to occur at a frequency at least as low as 70 kHz for a pH of about 4.2. This loss process is distinct from those arising from proton-transfer equilibria perturbations which are manifest at pH 3.2 and 11.6 and at peak frequencies of 400 kHz and above.