[The effect of calcium and magnesium ions on the interaction of calcium-binding proteins parvalbumin and alpha-lactalbumin with dipalmitoylphosphatidylcholine vesicles].

Interactions of the calcium binding proteins, like parvalbumins pI 4.2 and p15.0 and bovine and human alpha-lactalbumins, with dipalmitoylphosphatidylcholine vesicles have been studied by means of scanning microcalorimetry and intrinsic tryptophan, tyrosine and phenylalanine fluorescence. The interactions are modulated by the Ca2+ and Mg2+ binding to the proteins and induce some changes in the physical properties of both the proteins and the liposomes. The liposomes increase the thermal stability of the Mg2+-loaded and metal-free parvalbumin. Ca2+-loaded alpha-lactalbumin interacts with the liposomes in its native state, while the metal-free protein binds to the liposomes mainly in its thermally denatured state. The interactions of both proteins with the liposomes affect the phase transition from gel to liquid-crystalline state in the liposomes. The results of the microcalorimetric and spectrofluorometric studies are corroborated by the data obtained by means of gel-chromatography on Sepharose 4B.