Interaction of chlorpromazine with low molecular mass ion-transporting ATPase modulator proteins from rat brain cytosol

Abstract

Two low molecular mass proteins (13 kDa which inhibits Na⁺, K⁺-ATPase and 12 kDa which modulates Ca²⁺, Mg²⁺- and Ca²⁺-ATPases), purified from rat brain cytosol form complexes with chlorpromazine (CPZ) on incubation. The conformational characteristics of the proteins and their complex have been studied by comparing the fluorescence and CD spectra. The tryptophan fluorescence data show that the inhibitor-CPZ complex does not quench the fluorescence of Na⁺, K⁺ -ATPase significantly. CD spectra indicate that the structure of the inhibitor is changed on format ion of the complex. The inhibitor-CPZ complex significantly changes the conformation of Na⁺, K⁺-ATPase. The regulator protein-CPZ complex does not have any appreciable effect on Ca²⁺, Mg²⁺ - and Ca²⁺-ATPase activities. The Trp-fluorescence of Ca²⁺, Mg²⁺-and Ca²⁺-ATPases are not significantly affected in presence of the complex. CD spectra indicate that the structure of the regulator is abruptly affected on formation of the complex. The conformations of Ca²⁺, Mg²⁺-and Ca²⁺-ATPases are found to be altered in presence of the complex.