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. Interacts with nkain. In embryos, it is expressed in the neurons of the CNS and PNS, in Garland cells and posterior spiracles. In adults, it is concentrated in the thorax and abdomen (muscle tissue, digestive system and Malpighian tubules) and weakly expressed in the head. Expression is diffuse in the nervous system. Expression in embryos is first seen 12 hours after oviposition, peaks at 24 hours and decreases to a low level by 48 hours. Low levels are seen during larval and early pupal development. Levels increase during late pupae to maximal at the adult stage. Belongs to the X(+)/potassium ATPases subunit beta family.