Binding of sodium and potassium to the sodium pump of pig kidney evaluated from nucleotide‐binding behaviour.

Abstract

SUMMARY1. Using a rate-dialysis technique at 0-2 'C, the affinities of Na+ and K+ for the sodium pump of pig kidney outer medulla were determined from their effects on the binding of ADP to the enzyme.2. Since all experiments were carried out in the presence of Tris, the enzyme in absence of its specific ligands was assumed to be in a 'sodium-like' conformation.3. The model used in the analysis of the results assumed the enzyme to be a dimeric structure with two identical high-affinity nucleotide-binding sites. It is concluded from the data that the effects of Na+ and K+ on the binding of nucleotide to either subunit of a nucleotide-free enzyme are identical.4. The two subunits, taken together, have five identical and non-interacting K+-binding sites (KdjSS = 0 5 mM) whose occupation antagonizes nucleotide binding. 7. It is likely that the cation sites investigated are intracellular ones and it is concluded that the binding of each cation to its site induces a specific conformational change in the neighbourhood of the site itselfwithout affecting the regions around the remaining cation binding sites.

The Occlusion of Rb+ in the Na+/K+-ATPase

“…Enzyme-Na ϩ /K ϩ -ATPase was partially purified from pig kidney (15 Glynn and Chappell (16), except that no unlabeled orthophosphate (P i ) was added. All other reagents were of analytical grade.…”

An Attachment for Nondestructive, Fast Quenching of Samples in Rapid-Mixing Experiments

“…Na ϩ /K ϩ -ATPase was partially purified from pig kidney (13). The specific activity at the time of preparation was 23-25 mol Pi min Ϫ1 (mg protein) Ϫ1 , measured under optimal conditions (150 mM NaCl, 20 mM KCl, 3 mM ATP, 3 mM MgCl 2 , 25 mM imidazoleHCl, pH 7.4, at 37°C).…”

Are the States That Occlude Rubidium Obligatory Intermediates of the Na+/K+-ATPase Reaction?

“…ϩ /K ϩ -ATPase was partially purified from pig kidney (19). The specific activity at the time of preparation was 23-25 (mol P i ) min Ϫ1 (mg protein)…”