Comparative properties of sensitive to GABAA-ergic ligands, Cl(-), HCO3(-)-activated Mg2+-ATPase from brain plasma membranes of fish and rats

Action of Cl(-) + HCO3(-) ions on Mg2+-ATPase from brain plasma membranes of fish and rats has been studied. Maximal effect of the anions on the Mg2+-ATPase activity is revealed in the presence of 10 mM Cl(-) and 3 mM HCO3(-) at physiological values of pH of incubation medium. The studied Cl(-), HCO3(-)-activated Mg2+-ATPases of both animal species, by their sensitivity to SH-reagents (5,5-dithiobis-nitrobenzoic acid, N-ethylmaleimide), oligomycin, and orthovanadate, are similar to transport ATPase of the P-type, but differ from them by molecular properties and by sensitivity to ligands of GABAA-receptors. It has been established that the sensitive to GABAA-ergic ligands, Cl(-), HCO3(-)-activated Mg2+-ATPase from brain of the both animal species is protein of molecular mass around 300 kDa and of Stocks' radius 5.4 nm. In fish the enzyme is composed of one major unit of molecular mass approximately 56 kDa, while in rats--of three subunits of molecular masses about 57, 53, and 45 kDa. A functional and structural coupling of the ATP-hydrolyzing areas of the studied enzyme to sites of binding of GABAA-receptor ligands is suggested.