Conformational transitions of holo-alpha-lactalbumin in hydro-ethanolic solutions.

Spectroscopic and thermodynamic studies of holo-alpha-lactalbumin folding show that in hydro-ethanolic media this protein structure is subjected to at least three distinct transitions induced by ethanol. As observed by spectrofluorescence and circular dichroism (CD) the first transition is only local, being associated with changes in the state of aromatic chromophores. During this transition overall tertiary structure of alpha-lactalbumin is retained. As shown by high-sensitivity differential scanning calorimetry (HS-DSC) and CD, the second transition involves breakdown of the protein tertiary structure. The final organisation of the protein into highly helical folding may be considered as the third structural transition since the unfolding and the new helix formation are time-resolved processes.