[Study of the interaction of Na+,K+-ATPase protomers using the molecular target method].

The radiation inactivation analysis of Na+, K+-ATPase, (EC 3.6.1.37) from two different sources was carried out using ATP, CTP, GTP and p-NPP as substrates. In the case of Na+, K+-ATPase from the bovine brain the relation between the logarithm of the residual activity and the radiation dose is strictly linear, which permits calculating 75-90 kDa (for 3 mM GTP and 10 mM p-NPP). Duck salt glands Na+, K+-ATPase reveals larger target sizes: 350 kDa for ATP hydrolysis in saturating concentrations and 145-190 kDa in the case of GTP and p-NPP or low concentration of ATP (30 microM). A conclusion is drawn that while hydrolyzing substrates with complex kinetics (ATP and CTP) the enzyme functions like oligomer. The interaction of nucleotide with substrate-binding site of low affinity induces the aggregation of monomers.