A role for the beta-subunit in the expression of functional Na+-K+-ATPase in Xenopus oocytes

Am J Physiol. 1989 Nov;257(5 Pt 1):C851-8. doi: 10.1152/ajpcell.1989.257.5.C851.


In all cellular systems studied so far, the catalytic alpha- and the glycosylated beta-subunit of Na+-K+-ATPase are coordinately synthesized and are assembled into stoichiometric alpha, beta-complexes. In contrast to these data, in this study we show that the fully grown oocyte of Xenopus laevis synthesizes much less beta-subunit than alpha-subunit. The alpha-subunit produced in excess over the beta-subunit is membrane associated but highly trypsin sensitive and can be compared with the immature alpha-subunit population identified in epithelial cells immediately after synthesis (K. Geering, J. P. Kraehenbuhl, and B.C. Rossier, J. Cell Biol. 105: 2613-2619, 1987). The Xenopus oocyte thus turns out to be a unique system to study the functional role of the beta-subunit. Injection of beta-subunit-specific mRNA transcribed in vitro from a beta-cDNA clone (derived from Xenopus kidney, A6 cells) into oocytes results in translation of a glycosylated beta-subunit. The synthesis of this exogenous beta-subunit increases significantly the proportion of trypsin-resistant oocyte alpha-subunits able to perform cation-dependent conformational changes. In addition, 25-65% more ouabian binding sites are expressed at the plasma membrane in beta-mRNA-injected oocytes. In contrast, newly synthesized alpha-subunit translated after injection of size-fractionated mRNA enriched in alpha-mRNA remains trypsin sensitive as the oocyte alpha-subunit. These data suggest that association of the beta-subunit to the alpha-subunit provokes a structural rearrangement of the alpha-subunit that might be a first step toward the functional maturation of the Na+-K+-ATPase and its expression at the plasma membrane.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Membrane / enzymology
  • Drug Resistance
  • Female
  • Oocytes / enzymology
  • Oocytes / physiology*
  • RNA, Messenger / genetics
  • RNA, Messenger / pharmacology
  • Sodium-Potassium-Exchanging ATPase / biosynthesis
  • Sodium-Potassium-Exchanging ATPase / physiology*
  • Transcription, Genetic
  • Trypsin / pharmacology
  • Xenopus / physiology*


  • RNA, Messenger
  • Trypsin
  • Sodium-Potassium-Exchanging ATPase