Sodium pump

The sodium pump, or Na-K ATPase, is found in all cells. It is an integral membrane protein, formed by a tetrameric complex of two polypeptides: two transmembrane catalytic alpha subunits and two glycoprotein regulatory beta subunits.

The catalytic subunits form the gated channel and possess binding sites for Na+ and adenosine S'-triphosphate (ATP) on the intracellular surface, and for K+ and ouabain on the extracellular surface. They have phosphorylation sites and span the plasma membrane ten times. The beta subunit comprises a single membrane-spanning domain and has three extracellular glycosylation sites.

It requires oxygen for the provision of the substrate, ATP. It is electrogenic, extruding 3 Na+ ions for every 2 K+ ions (coupling ratio of 3:2). The pump is an antiport, transporting two different ions in opposite directions across the membrane. Sodium Na+ ion pumped out of the cell is used to drive active co-transport systems.

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