[Protein globule without the unique three-dimensional structure: experimental data for alpha-lactalbumins and general model].

It has been shown that bovine and human alpha-lactalbumins under the influence of acidic pH, high temperatures or low guanidine hydrochloride concentrations are transferred into a state which is quite distinct both from the native and the completely denatured (unfolded) ones. Human alpha-lactalbumin can be transferred into this intermediate state also by removal of the bound to it Ca2+ ion. On the basis of the obtained physical characteristics of this state a model of the "intermediate" state is suggested in which a protein globule is compact, has a secondary structure, but does not possess a unique three-dimensional structure. Phase diagrams of the protein molecule states (native, intermediate and unfolded) are presented and discussed and the role of the intermediate state in protein folding is considered.