Molecular analysis of terminal oxidases in electron-transport pathways of Bradyrhizobium japonicum and Azotobacter vinelandii

  • R. J. Maier
  • F. Moshiri
  • R. G. Keefe
  • C. Gabel


Both B. japonicum and A. vinelandii contain branched electron transport pathways, utilizing multiple terminal oxidases. The oxidases display differing affinities for O2, thus allowing the O2 concentration to regulate the pathway of electron flow- It is thought that the roles the multiple oxidases play in N2 fixation may be to permit both coupled ATP-synthesizing, and uncoupled but O2-scavenging electron transport (respiratory protection, see ref. 20). Indeed, inhibitor studies on both N2-fixing Azotobacter (9,10,20) and bacteroids of B. japonicum (3–7) suggest the presence of highly-efficient ATP-synthesizing and inefficient O2-scavenging pathways. The O2 concentration at the bacterial membrane then is the factor determining the use of the coupled versus uncoupled pathways. It is important to keep in mind that the free O2 level in root nodules is maintained primarily by leghemoglobins, so that even the highest O2 levels at the bacteroid surface are much less than fully aerobic.


Nitrogen Fixation Oxidase Activity Bradyrhizobium Japonicum Terminal Oxidase Azotobacter Vinelandii 
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Copyright information

© Routledge, Chapman & Hall, Inc. 1990

Authors and Affiliations

  • R. J. Maier
    • 1
  • F. Moshiri
    • 1
  • R. G. Keefe
    • 1
  • C. Gabel
    • 1
  1. 1.Department of BiologyThe Johns Hopkins UniversityBaltimoreUSA

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