Principles of selectivity of sodium and potassium binding sites of the Na+/K+-ATPase. A corollary hypothesis.
The mechanisms whereby the sodium and potassium binding sites of heart sacrolemmal Na+/K+-ATPase (EC 3.6.1.3) distinguished between monovalent cations were investigated using methods of enzyme kinetics. The properties of the sodium binding sites were studied in the presence of 2,4,6-trinitrobenzenesulfonic acid in concentrations completely inhibiting the action of potassium on the enzyme. To test the selectivity of potassium binding sites, K+-p-nitrophenylphosphatase activity was employed as a model. The results suggest that the selectivity of Na+- and K+-binding sites of Na+/K+-ATPase may be due to two independent mechanisms: (i) The principle of key and lock (formation of coordination bounds); (ii) Optimal difference between solvatation energy (in the specific binding site) and hydration enthalpy of the respective cation.
Breier
A
A
Centre of Physiological Sciences, Slovak Academy of Sciences, Bratislava, Czechoslovakia.
Nagy
L T
LT
Ziegelhöffer
A
A
Monosíková
R
R
D000818:Animals; D001665:Binding Sites; D008433:Mathematics; D008956:Models, Chemical; D009206:Myocardium / Q000201:enzymology; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D012508:Sarcolemma / Q000201:enzymology; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium