INTERACTION OF POLYAMINES WITH THE CA2-BINDING PROTEIN PARVALBUMIN()

The interaction of spermine, spermidine and putrescine with the Ca2+-b inding protein, parvalbumin, was studied at pH 6 and 7, with the help of the intrinsic fluorescence properties of tryptophan and circular di chroic spectroscopy of the protein in the ultraviolet region. Polyamin es bind to parvalbumin that is either Ca2+-free or partially saturated with Ca2+, as indicated by a change in the emission maximum and inten sity of tryptophan fluorescence. The binding affinities for the intera ctions are about 4 mM, 8 mM and > 20 mM for spermine, spermidine and p utrescine, respectively. No alterations in fluorescence properties wer e detected when the polyamines were added to fully Ca2+-bound parvalbu min. An increase in the ellipticity of the circular dichroic spectrum in the region where tryptophan absorbs was observed when polyamines we re added to Ca2+-free parvalbumin. This finding indicates that polyami ne binding affects the segment of the protein where tryptophan is loca ted. Based on these results it is postulated that polyamines bind to t he Ca2+-free of partially saturated parvalbumin and stabilize its stru cture.