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, liver, lung, kidney, heart, brain and skin. 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.