Adenosine triphosphate-dependent retention of sodium ions by a sodium and potassium-activated adenosine triphosphatase preparation from erythrocyte membranes

In plasma membranes of intact cells an enzymatic pump actively transports sodium ions inward and potassium ions outward. In preparations of broken membranes it appears as an adenosine triphosphatase dependent on magnesium, sodium, and potassium ions together. In this adenosine triphosphatase a phosphorylated intermediate is formed from adenosine triphosphate in the presence of sodium ions and is hydrolyzed with the addition of potassium ions. The normal intermediate was not split by adenosine diphosphate. However, selective poisoning by N-ethylmaleimide or partial inhibition by a low magnesium ion concentration yielded an intermediate split by adenosine diphosphate and insensitive to potassium ions. Pulse experiments on the native enzyme supported further a hypothesis of a sequence of phosphorylated forms, the first being made reversibly from adenosine triphosphate in the presence of sodium ion and the second being made irreversiblyfrom the first and hydrolyzed in the presence of potassium ion. The cardioactive steriod inhibitor, ouabain, appeared to combine preferentially with the second form. Phosphorylation was at the same active site according to electrophoretic patterns of proteolytic phosphorylated fragments of both reactive forms. It is concluded that there is a conformational change in the active center for phosphorylation during the normal reaction sequence. This change may be linked to one required theoretically for active translocation of ions across the cell membrane.

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Nucleophilic behavior of lysine-501 of the .alpha.-polypeptide of sodium and potassium ion activated adenosine triphosphatase consistent with a role in binding adenosine triphosphate

Biochemistry ◽

10.1021/bi00433a041 ◽

1989 ◽

Vol 28 (7) ◽

pp. 3009-3017 ◽

Cited By ~ 8

Author(s):

Kai Yuan Xu ◽

Jack Kyte

Keyword(s):

Adenosine Triphosphate ◽

Adenosine Triphosphatase ◽

Potassium Ion ◽

Sodium And Potassium

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The influence of external sodium ions on the sodium pump in erythrocytes

Biochemical Journal ◽

10.1042/bj1090369 ◽

1968 ◽

Vol 109 (3) ◽

pp. 369-374 ◽

Cited By ~ 39

Author(s):

R. N. Priestland ◽

R. Whittam

Keyword(s):

Adenosine Triphosphatase ◽

Sodium Pump ◽

Erythrocyte Membranes ◽

Sodium Ions ◽

Adenosine Triphosphatase Activity ◽

Sensitive Site ◽

Na Efflux ◽

Ion Movements ◽

K Concentration ◽

External K

1. A study has been made of the interaction between Na+ and K+ on the adenosine triphosphatase activity of erythrocyte ‘ghosts’, and on the K+ influx and Na+ efflux of intact erythrocytes. The adenosine triphosphatase activity and the ion movements were greater at a low external K+ concentration in the absence of Na+ than they were in the presence of 150mm-Na+. The inhibition by external Na+ of K+ influx had an inhibitory constant of 5–10mm. 2. Activation by K+ of kidney microsomal adenosine triphosphatase was retarded by Na+, and activation by Na+ was retarded by K+. Fragmented erythrocyte membranes behaved similarly. 3. These observations suggest that there is competition between Na+ and K+ at the K+-sensitive site of the membrane.

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