Functional modulation of the sodium pump: the regulatory proteins "Fixit".

Proteins of the FXYD family act as tissue-specific regulators of the Na-K-ATPase. They are small hydrophobic type I proteins with a single-transmembrane span containing an extracellular invariant FXYD sequence. FXYD proteins are not an integral part of the Na-K-ATPase but function to modulate its catalytic properties by molecular interactions with specific Na-K-ATPase domains.