Aspects of the oxygen-tolerance of nitrogen fixation in Azotobacter vinelandii

G.H. Scherings

Research output: Thesisinternal PhD, WU


Following the pioneering physiological studies of Haaker <em>et al.</em> on the generation of reducing equivalents for nitrogenase in <em>Azotobacter</em><em>vinelandii,</em> it seemed desirable to further characterize interactions between the likely ultimate electron donors (flavodoxin and/or ferredoxin) and nitrogenase. Isolation of these proteins was therefore necessary. Flavo- and ferredoxin from <em>A.vinelandii</em> have been prepared to purity; as far as nitro genase was concerned, however, it was deemed that the O <sub><font size="-1">2</font></sub> -tolerant nitrogenase complex as isolated originally by Bulen and LeComte should render information more physiologically relevant than could be the case using highly puri fied nitrogenase components (Av <sub><font size="-1">1</font></sub> + Av <sub><font size="-1">2</font></sub> ). In chapter II, results are described suggesting that the Bulen-LeComte nitrogenase complex, with fully reduced fla vodoxin as a source of reducing equivalents, has regulatory properties not exhibited by a more highly purified (Av <sub><font size="-1">1</font></sub> + Av <sub><font size="-1">2</font></sub> ) complex, due to the presence of a 'contaminating' third protein.<p/>This third protein appeared to be the same as that shown by Haaker <em>et</em><em>al.</em> to be responsible for the oxygen-tolerance of the nitrogenase complex. The spectral properties and molecular weight are shown in chapter II to be identical to that of the [2Fe-2S] ferredoxin isolated earlier by Shethna <em>et</em><em>al.</em> who, however, did not ascribe any physiological function to this pro tein. In chapters III and IV, the interactions between Av <sub><font size="-1">1</font></sub> , Av <sub><font size="-1">2</font></sub> and the third protein are further characterized, as well as the conditions necessary to induce the reconstitution of an oxygen-tolerant complex from the purified proteins. The relation between the oxygen-tolerant complex and the so-called 'switched-off state' of nitrogenase activity <em>in vivo</em> is discussed.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Veeger, C., Promotor
  • Haaker, H.B.C.M., Co-promotor, External person
Award date21 Dec 1983
Place of PublicationWageningen
Publication statusPublished - 1983


  • azotobacter
  • pseudomonadaceae
  • microbiology
  • nitrogen cycle

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