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. In embryos, it is expressed in the neurons of the CNS and PNS, in Garland cells and posterior spiracles. In adults, it shows a nervous system specific distribution: optic lobes, brain, thoracic ganglia and axonal pathways in the leg. Both isoforms concentrate in the adult head, isoform 2.2 being predominant. Both isoforms are weakly expressed in the thorax and very poorly expressed in the abdomen. 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.