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Pflügers Archiv

, Volume 381, Issue 2, pp 127–135 | Cite as

Substructure of membrane-bound Na+−K+-ATPase protein

  • W. Haase
  • H. Koepsell
Transport Processes, Metabolism and Endocrinology; Kidney, Gastrointestinal Tract, and Exocrine Glands

Abstract

Purified membrane-bound Na+−K+-ATPase from rat kidney outer medulla was studied by freeze-fracturing, by freeze-etching and by negative staining. Freeze-fracturing of purified Na+−K+-ATPase membranes shows intramembraneous particles with a diameter of about 100 Å. The frequency of these intramembraneous particles — as estimated from the particle densities on the two fracture faces — lies between 4700 and 5600 particles per μm2. Applying rotary shadowing a four partite substructure could be detected in these intramembraneous particles observed on the fracture planes. The same four partite substructure was detected in particles observed on freeze-fractured and rotary shadowed intact baso-lateral plasma membranes of the thick ascending limb of Henle's loop. Particles could be also detected on both membrane surfaces of the purified Na+−K+-ATPase. These surface particles have about the same diameter and are present at about the same frequency as those observed within the freeze-fractured membranes. Negative staining of isolated Na+−K+-ATPase membranes showed particles on both membrane surfaces with a diameter between 30 and 50 Å, at a frequency of about 19,000 per μm2. On aspects of membrane edges we observed structures which suggest a transmembraneous connection of the negatively stained particles on both membrane surfaces.

Our results suggest that the Na+−K+-ATPase protein is composed of four units and that each unit spans the cell membrane. The native enzyme structure of the Na+−K+-ATPase protein seems to be preserved during freeze-fracturing and freeze-etching. It is proposed that the four enzyme units of the Na+−K+-ATPase complex are dissociated during the negative staining procedure.

Key words

Na+−K+-ATPase Rat kidney Electron microscopy Substructure 

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Copyright information

© Springer-Verlag 1979

Authors and Affiliations

  • W. Haase
    • 1
  • H. Koepsell
    • 1
  1. 1.Max-Planck-Institut für BiophysikFrankfurt am MainFederal Republic of Germany

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