THE EXTRACELLULAR DOMAIN OF THE SODIUM-PUMP BETA-ISOFORMS DETERMINES COMPLEX STABILITY WITH ALPHA-1

Both subunits of the Na,K-ATPase are encoded by several genes giving r ise to at least six isozymes. To examine whether beta isoforms assembl e with alpha 1 in a selective manner, we have overexpressed wild-type and chimeric beta subunits in L929 cells and examined assembly as a fu nction of resistance towards detergent-mediated dissociation. In the p resence of digitonin all beta chimeras coimmunoprecipitate the endogen ous alpha 1 subunit. Only beta proteins with the ectodomain of beta 1 coimmunoprecipitate alpha 1 in the presence of Triton X-100. All beta chimeras stimulate Na,K-ATPase activity in L929 cells. These data indi cate that the beta subunit ectodomains mediate interactions with alpha 1 and influence the stability of this complex. (C) 1997 Academic Pres s.