European Journal of Biochemistry vol:218 issue:2 pages:303-309
The effects of polyamines on the spectral properties and thermal stability of different alpha-lactalbumins were measured. Addition of millimolar concentrations of spermine to the Ca2+-free (apo) form of bovine or goat alpha-lactalbumin resulted in spectral shifts, in both the far- and near-ultraviolet ranges, similar to those induced by Ca2+ binding. Fluorescence emission spectra of tryptophan residues underwent a pronounced blue shift, concomitant with a decrease in quantum yield. Also, in the presence of spermine. thermal stability was increased. In contrast, in the case of human and to some extent also equine alpha-lactalbumin, the shifts of the CD and fluorescence spectra and the thermal denaturation curves were in the opposite direction.