NaKpomp

NaKpomp, short for the sodium-potassium pump, is an essential membrane-bound enzyme (Na+/K+-ATPase) found in the plasma membrane of nearly all animal cells. Using energy from ATP hydrolysis, it actively transports three Na+ ions out of the cell and two K+ ions into the cell per cycle, maintaining steep gradients of these ions across the membrane. This gradient underpins the resting membrane potential, regulates cell volume, and powers secondary active transport processes.

Mechanistically, the pump alternates between inward-facing (E1) and outward-facing (E2) conformations. Binding of Na+ on the cytoplasmic side, phosphorylation of the α-subunit by ATP hydrolysis, and subsequent conformational change drive Na+ release to the extracellular space. Binding of extracellular K+ stimulates dephosphorylation and return to the original state, releasing K+ into the cytoplasm and readying the pump for another cycle. The α-subunit is the catalytic component, and it associates with β- and sometimes γ-subunits that influence trafficking and activity. In many vertebrates the pump is inhibited by cardiac glycosides such as ouabain and digoxin, which bind to the extracellular face of the α-subunit.

Physiological and clinical relevance: The Na+/K+-ATPase is essential for nerve impulse transmission and muscle contraction, maintains cellular water balance, and provides the Na+ gradient that drives secondary transport of nutrients and electrolytes in tissues such as the kidney and intestine. Tissue-specific isoforms of the α-subunit allow variation in expression and kinetics across organs. Dysfunction or altered expression of the pump is associated with a range of conditions and is a focus of pharmacological and physiological research.