This is the non-catalytic component of the active enzyme, which catalyzes the hydrolysis of ATP coupled with the exchange of Na(+) and K(+) ions across the plasma membrane. Composed of two subunits: alpha (catalytic) and beta (accessory). Expressed in skeletal muscle, intestine, heart, brain, retina, inner ear and skin. Expressed in embryo in skeletal muscle, heart, brain, retina, inner ear and skin at 19 dpc. Glycosylated. Its function as a Na,K-ATPase beta-subunit will be lost in placental mammals. Belongs to the X(+)/potassium ATPases subunit beta family.