CONFORMATIONAL TRANSITIONS OF HOLO-ALPHA-LACTALBUMIN IN HYDRO-ETHANOLIC SOLUTIONS

Spectroscopic and thermodynamic studies of holo-alpha-lactalbumin fold ing show that in hydro-ethanolic media this protein structure is subje cted to at least three distinct transitions induced by ethanol. As obs erved by spectrofluorescence and circular dichroism (CD) the first tra nsition is only local, being associated with changes in the state of a romatic chromophores. During this transition overall tertiary structur e of alpha-lactalbumin is retained. As shown by high-sensitivity diffe rential scanning calorimetry (HS-DSC) and CD, the second transition in volves breakdown of the protein tertiary structure. The final organisa tion of the protein into highly helical folding may be considered as t he third structural transition since the unfolding and the new helix f ormation are time-resolved processes.