SEQUENTIAL HYDRATION OF DRY PROTEINS - A DIRECT DIFFERENCE IR INVESTIGATION OF SEQUENCE HOMOLOGS LYSOZYME AND ALPHA-LACTALBUMIN

Direct difference IR spectra are presented as a function of hydration for [hen egg] lysozyme and [bovine milk] .alpha.-lactalbumin, and detailed sequential hydration molecular events identified. Despite the strong sequence homology between the 2 proteins, and their expected conformational similarity, the hydration behavior, of the polar groups is different for the 2 proteins. A Hill-type analysis suggested that the acid groups ionize and hydrate rapidly and noncooperatively in both proteins, consistent with the known (lysozyme) and postulated (.alpha.-lactalbumin) surface chemistry. The polar group hydration shows a clear cooperativity relates to a hydration-induced loosening up of the lysozyme conformation at about 55 mol water/mol protein. .alpha.-Lactalbumin appears to open up more easily for hydration than does lysozyme, consistent with its lower stability against thermal and acid denaturation.