In this work we have shown the first application of the ultrafast, laser induced pH jump methodology with photoacoustic detection to the study of the early events in the unfolding of a protein.
Besides protonation of sites on the protein, our data evidence a sequential step where a substantial solvation of structure occurs and represents a rate limiting step in the formation of the compact acid intermediate.  This rate constant is comparable with the rate recently measured by means of lasr-T-jump coupled with tryptophan fluorescence emission detection (Ballew, R. M., J. Sabelko and M. Gruebele (1996). Nature Struct. Biol. 3: 923-926) for the formation of the subdomain including helices A, G and H.
The thermodynamic parameters (volume change, enthalpy change and activation energy) of this reaction show that the interaction between his24 and his119 represents a key  interaction in stabilizing N with respect to I.