[Study of catalytically active center of the Ca2+-Mg2+-dependent ATPase of sarcoplasmic reticulum by triplet probe method]

It was shown that eosine and erythrosine are competing inhibitors of the Ca2+-Mg2+- dependent ATPase active center of sarcoplasmic reticulum. The eosine and erythrosine inhibition constants are equal to 1.4 x 10(-6) M and 1.1 x 10(-6) M, respectively. Nitroxide radicals of various hydrophobicity and K3Fe(CN)6 were used to compare the constants of triplet states exchange quenching of erythrosine in aqueous solution, in lecithine liposomes and in ATPase active center of sarcoplasmic reticulum. It was established that ATPase binding center was immersed into a liquid phase and was not connected with lipids. Mn2+ and Gd3+-ions, which are competing with Mg2+ and Ca2+ for binding sites in the enzyme active center, diminished the phosphorescence quenching time of eosine at 77K. This means that the ion binding sites are less than 12 A apart from ATP-binding center.