[Troponin from th bovine heart: isolation and study of cation-binding properties using a...

A method for isolation of bovine heart troponin has been developed. The troponin complex was separated into constituent components. The fluorescent probe 3-dimethylaminonaphtheurodine binds to heart troponin: the fluorescence of the troponin--dimethylaminonaphtheurodine complex is increased with a rise in Ca2+ concentration from pCa 8 to pCa 5. The apparent constant for Ca2+ binding to heart troponin calculated from the changes in fluorescence of the troponin-dimethylaminonaphtheurodine complex is equal to 2,1 . 10(6) M(-1). The corresponding constant for Sr2+ binding by heart troponin is 5 . 10(5) M(-1), Mg2+ have no effect on Ca2+ and Sr2+ binding. The results obtained suggest that heart troponin contains Ca-specific binding sites and that the binding of Ca2+ to these sites evokes conformational changes, which are registered by means of the fluorescent probe. The Hill coefficient for the conformational changes of heart troponin induced by Ca2+ and Sr2+ measured with the probe is equal to unity. The use of 3-dimethylaminonaphtheurodine as a marker of conformational changes allows to compare the cation-binding properties of troponin from heart and skeletal muscles.