An Investigation of the Conformation of Bovine α‐Lactalbumin by Proton Magnetic Resonance and Optical Spectroscopy

Proton magnetic resonance spectra are reported of α‐lactalbumin at 100 and 220 MHz. The extensive sequence homologies between this protein and lysozyme have led to the postulate of a close conformational similarity. Our results on optical rotatory dispersion, circular dichroism and infrared spectra of the two proteins are consistent with this hypothesis. The proton magnetic resonance spectra of the native proteins show differences in the upfield region of the spectrum associated with aliphatic side chain protons. Calculations of ring‐current shifts induced in these protons, in terms of the atomic coordinates for the putative α‐lactalbumin structure, as fitted by Phillips and co‐workers to the lysozyme model, account semi‐quantitatively for the observed spectrum. The discrepancies between the α‐lactalbumin and lysozyme spectra are, moreover, almost wholly explicable in terms of specific sequence differences between the two proteins.