Comparison of protein structure in crystals, in lyophilized state, and in solution by laser Raman scattering. III. .alpha.-Lactalbumin

Possible conformational changes of α-lactalbumin associated with lyophilization and crystallization were investigated in detail by Raman scattering technique It was found that lyophilization altered the protein three-dimensional structure considerably, but crystallization produced no detectable effect on backbone conformation. This conclusion is the same as that reached earlier for lysozyme. In the amide III region (both crystals and solution spectra) three well-defined peaks were observed at 1274, 1260, and 1238 cm-1 very similar to those of lysozyme at 1272, 1258, and 1238 cm-1, respectively, indicating that α-lactalbumin may have a conformation similar to that of hen's egg-white lysozyme. This is consistent with the “analogy” molecular model proposed by Browne, et al. To demonstrate the sensitivity of the amide III contour with respect to change in α-lactalbumin backbone conformation, Raman spectra of aqueous solution at pH 6.6 and 2.1 were compared. Spectral evidence was presented that the distinct feature of an extremely sharp peak at 1361 cm-1 in both α-lactalbumin and lysozyme was related to some specific interactions involving those “buried” indole rings.