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Journal ArticleDOI

Effects of intracellular adenosine-5'-diphosphate and orthophosphate on the sensitivity of sodium efflux from squid axon to external sodium and potassium.

01 Nov 1970-The Journal of General Physiology (The Rockefeller University Press)-Vol. 56, Iss: 5, pp 583-620
TL;DR: An outline is presented for a model which might explain the effects of ADP, Pi and deoxy-ATP, and it is shown that sodium efflux is maximally Ko-dependent when the ATP:ADP ratio is about 10:1, becomes insensitive to Ko when the ratios are about 1:2, and is inhibited byKo when the ratio isAbout 1:10.
Abstract: A study was made of sodium efflux from squid giant axon, and its sensitivity to external K and Na. When sodium efflux from untreated axons was strongly stimulated by Ko, Nao was inhibitory; when dependence on Ko was low, Nao had a stimulatory effect. Incipient CN poisoning or apyrase injection, which produces high intracellular levels of ADP1 and Pi, rendered sodium efflux less dependent on external K and more dependent on external Na. Injection of ADP, AMP, arginine, or creatine + creatine phosphokinase, all of which raise ADP levels without raising Pi levels, had the same effect as incipient CN poisoning. Pi injection had no effect on the K sensitivity of sodium efflux. Axons depleted of arginine and phosphoarginine by injection of arginase still lost their K sensitivity when the ATP:ADP ratio was lowered and regained it partially when the ratio was raised. Rough calculations show that sodium efflux is maximally Ko-dependent when the ATP:ADP ratio is about 10:1, becomes insensitive to Ko when the ratio is about 1:2, and is inhibited by Ko when the ratio is about 1:10. Deoxy-ATP mimicked ADP when injected into intact axons. Excess Mg, as well as Pi, inhibited both strophanthidin-sensitive and strophanthidin-insensitive sodium efflux. An outline is presented for a model which might explain the effects of ADP, Pi and deoxy-ATP.

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Citations
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Journal ArticleDOI
TL;DR: It was concluded that adenosine triphosphate was activating the enzyme in a fashion functionally distinct from its action as a phosphate donor, since the concentration of adenosines triph phosphate required for activation was much higher than that required for phosphorylation.

809 citations

Book ChapterDOI
01 Jan 1985
TL;DR: The Na+-transporting adenosine triphosphatase (Na+,K+-ATPase), also often known as the sodium pump or sodium-potassium pump, is an enzyme that uses energy from the hydrolysis of intracellular ATP to transport Na+ ions outwards and K+ ions inwards.
Abstract: The Na+,K+-transporting adenosine triphosphatase (Na+,K+-ATPase), also often known as the sodium pump or sodium-potassium pump, is an enzyme, found in nearly all animal-cell membranes, that uses energy from the hydrolysis of intracellular ATP to transport Na+ ions outwards and K+ ions inwards. It may be thought of as having three substrates (ATP, intracellular Na+ ions, and extracellular K+ ions) and four products (ADP, orthophosphate, extracellular Na+ ions, and intracellular K+ ions.) Because more Na+ ions are pumped out than K+ ions are pumped in, the activity of the enzyme generates an outward movement of positive charge, and this outward current may also be considered a “product” of the reaction.

274 citations

Journal ArticleDOI
Jens Chr. Skou1
TL;DR: It seems to be the membrane bound (Na + +K + )-activated enzyme system which transforms the energy from a hydrolysis of ATP into a vectorial movement of sodium out and potassium into the cell against electrochemical gradients.
Abstract: It seems to be the membrane bound (Na++K +)-activated enzyme system which transforms the energy from a hydrolysis of ATP into a vectorial movement of sodium out and potassium into the cell against electrochemical gradients, i.e. this systems seems to be the transport system for sodium and potassium (see, for example, review by Skou, 1972; Hokin & Dahl, 1972).

259 citations

Journal ArticleDOI
TL;DR: A model for the sodium pump is proposed in which conformational changes alternate with trans-phosphorylations, and the inward and outward fluxes of both Na+ and K+ each involve the transfer of a phosphoryl group as well as a change in conformation between E1 and E2 forms of the enzyme or phosphoenzyme.

213 citations

Journal ArticleDOI
02 Apr 1993-Science
TL;DR: Measurement of the undirectional sodium-22 efflux mediated by Nai-Nao exchange demonstrates that the release and rebinding of external sodium is the predominant charge-moving step, suggesting that extracellular sodium ions must reach their binding sites deep in the pump molecule through a high-field access channel.
Abstract: In each normal Na,K pump cycle, first three sodium and then two potassium ions are transported; in both cases, the ions become temporarily occluded in pump conformations that isolate them from internal and external solutions. A major charge movement occurs during sodium translocation and accompanies the deocclusion of sodium ions or their release to the cell exterior, or both. The nature of the charge movement was examined by measurement of the undirectional sodium-22 efflux mediated by Nai-Nao exchange (Nai and Nao are internal and external sodium ions) in voltage-clamped, internally dialyzed squid giant axons in the absence of potassium; in this way the pump activity was restricted to the sodium-translocation pathway. Although electroneutral, the Nai-Nao exchange was nevertheless voltage-sensitive: increasingly negative potentials enhanced its rate along a saturating sigmoid curve. Such voltage dependence demonstrates that the release and rebinding of external sodium is the predominant charge-moving (hence, voltage-sensitive) step, suggesting that extracellular sodium ions must reach their binding sites deep in the pump molecule through a high-field access channel. This implies that part of the pump molecule is functionally analogous to an ion channel.

184 citations