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. The beta subunit regulates, through assembly of alpha/beta heterodimers, the number of sodium pumps transported to the plasma membrane. The sodium/potassium-transporting ATPase is composed of a catalytic alpha subunit, an auxiliary non-catalytic beta subunit and an additional regulatory subunit. Detected in all tissues except liver and cardiac muscle. Highest levels found in intestine, ovary and kidney with marginally lower levels in brain, spleen, esophagus, eye and pancreas, intermediate levels in gill and low levels in white and red skeletal muscle. Belongs to the X(+)/potassium ATPases subunit beta family.