Correlation of hydrogen exchange behaviour and thermal stability of lysozyme

The solvent exchange rates of individual indole NH hydrogens of tryptophan residues of lysozyme have been measured, by using 1H nuclear magnetic resonance spectroscopy, as a function of temperature in the presence of urea and following chemical modification. The results have been interpreted in terms of a low activation energy process which is not dependent on the thermal stability of the protein, and a higher activation energy process that is directly correlated with the thermal stability. The significance of these observations for an understanding of the dynamics of the protein is discussed.