The effect of Mg2+ and ouabain on the incorporation of P32 from γ-ATP32 into Na+-and K+-activated adenosine triphosphatase

Charnock, John S.; Potter, H.A.

doi:10.1016/0003-9861(69)90248-3

Cited by 15 publications

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References 24 publications

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“…Considerable evidence indicates that ouabain inhibits ATPase by binding to the phosphorylated form of the enzyme but does not interfere with its formation [7,34]. The Na+-stimulated phosphorylation reaction is not inhibited by oligomycin nor NEM and it does not show inhibition by ouabain at low concentrations.…”

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Harmaline: A competitive inhibitor of Na Ion in the (Na++K+)-ATPase system

Canessa

Jaimovich

1973

J. Membrain Biol.

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Summary. Experimental evidence is given that the hallucinogen harmaline (HME) behaves as an inhibitor of the (Na+ § system, specifically in the Na +-dependent phosphorylation reaction. HME at 0.3 to 3 mM inhibited several membrane ATPase preparations such as those from human erythrocytes, rat brain and squid retinal axons. The same concentration blocked Na + outflow from squid giant axons. The behavior of several harmane derivatives such as harmine, harmalol and harmaline demonstrated that certain groups influenced the concentration for 50 % inhibition of the ATPase system. The following evidence demonstrated that HME blocked the formation of the phosphorylated intermediate by competition with Na ions in the (Na + +K+)-ATPase reaction in rat brain. (1) The HME effect on the overall (Na++ K+)-ATPase reaction showed a fully competitive inhibition with respect to Na ion concentration.(2) The inhibition of the Na+-stimulated phosphorylation by HME was fully competitive with respect to Na ions, with or without oligomycin present. (3) HME inhibited the effect of ADP on the phosphorylation reaction using 32p-ATP. (4) HME did not accelerate the rate of membrane dephosphorylation by means of 32p-ATP and cold ATP.From the behavior of HME as a competitive inhibitor at Na ion sites of the (Na + + K+)-ATPase reactions one may gain information about (a) The chemical nature of Na + sites which may be responsible for the selectivity of this cation, and (b) The sequence of Na + and ATP entrance into the Na+-dependent phosphorylation reaction. The experimental evidence supports the hypothesis that the entrance of Na + into the enzyme system may precede the formation of the phosphorylated intermediate.An interest in elucidating the nature of the molecular mechanism involved in the functioning of the sodium pump has led to the study of its behavior in isolated membrane fragments [1,6] and in intact cells [13,15]. From experiments with fragments of cell membranes with (Na + +K § ATPase activity, several partial reactions have been described. The reaction sequence appears to involve a Na+-stimulated phosphorylation of the enzyme followed by a K+-dependent dephosphorylation [29].IS J. Membrane Biol, 13

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Harmaline: A competitive inhibitor of Na Ion in the (Na++K+)-ATPase system

Canessa

Jaimovich

1973

J. Membrain Biol.

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Zum aktiven Na⁺, K⁺‐Transport durch die Membran tierischer Zellen

Schoner

1971

Angewandte Chemie

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Der Transport von N a + aus der Zelle und von K + in die Zelle entgegen einem Konzentrationsgradienten wird durch eine (Na' +-K+)-aktivierte ATPase katalysiert. Wie die Kationen die Zellmembran durchdringen, ist bisher ungeklart. Beim Studium der ATP-Hydrolyse durch das Enzym fand sich eine Na+-abhangige Phosphorylierung des Enzymproteins : zusatzlich scheint sich seine Konformation zu andern. Bei der K+-abhangigen Hydrolyse des enzyrngebundenen Phosphats wird wahrscheinlich die Energie fir den Transport der Kationen entgegen ihrem Konzentrationsgradienten frei. Durch Umkehr des Kationen-Konzentrationsgradienten kann das Enzym A T P aus anorganischem Phosphat und ADP synthetisieren. Das Herzglykosid Strophanthin hemmt die Na+-Pumpe spezijisch, indem es das Enzym in einer Konformation festhalt.

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