© 1995 Oxford University Press
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The head structure of a higher plant V-type H+–ATPase is not always a hexamer but also a pentamer1
2Institut für Botanik (FB 10), Technische Hochschule Darmstadt Schnittspahnstraße 3-5, D-64287 Darmstadt, Germany
3Abteilung für Akustik, Lernen und Sprache, Institut für Neurobiologie Brenneckestraß 6, D-39118 Magdeburg, Germany
4To whom correspondence should be addressed. Fax: + 49 6151 16 46 30.
Pentameric head structures of the V-type H+–ATPase of Mesembryanthemum crystallinum L. were demonstrated in addition to hexameric head structures by rotational image analysis and molecular projections of negatively stained H+–ATPase heads. This observation, at least partially, is in contrast to the standard model of the V-type H+–ATPase predicting solely a hexameric head structure with three A and three B subunits in analogy to the F-type ATPases. With one A or B subunit missing two A or two B subunits would be adjacent to each other in the pentameric ATPase head. By chemical cross-linking of H +–ATPase subunits a crosslinking product exclusively consisting of B subunits, in addition to a cross-linking product consisting of subunits A and B was detected. Thus, the pentameric heads might lack one A subunit, although the lack of one B subunit can not be totally ruled out. We assume that the hexameric head structure is the catalytically active configuration while the pentameric head structure may be a relatively stable intermediate of turnover.
Key words: V-type H+–ATPase, protein structure, electron microscopy, tonoplast, Mesembryanthemum crystallinum L