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Activation of Inactive Nitrogenase by Acid-Treated Component I

Department of Bacteriology, College of Agricultural and Life Sciences, University of Wisconsin, Madison, Wisconsin 53706

ABSTRACT

When Azotobacter vinelandii was derepressed for nitrogenase synthesis in a N-free medium containing tungstate instead of molybdate, an inactive component I was synthesized. Although this inactive component I could be activated in vivo upon addition of molybdate to the medium, it could not be activated in vitro when molybdate was added to the extracts. Activation occurred, however, when an acid-treated component I was added to extracts of cells derepressed in medium containing tungstate. Acid treatment completely abolished component I activity. Mutant strains UW45 and UW10 were unable to fix N₂. Both strains synthesized normal levels of component II but produced inactive component I. Acid-treated component I activated inactive component I in extracts of mutant strain UW45 but not mutant strain UW10. This activating factor could be obtained from N₂-fixing Klebsiella pneumoniae, Clostridium pasteurianum, and Rhodospirillum rubrum.

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