nitrogenase and ammonium-nitrate

The control of nitrogenase recovery from inactivation by oxygen was studied in Anabaena sp. strain CA (ATCC 33047). Nitrogenase activity (acetylene reduction) in cultures grown in 1% CO2 in air was inhibited by exposure to 1% CO2-99% O2 and allowed to recover in the presence of high oxygen tensions. Cultures exposed to hyperbaric levels of oxygen in the presence of 10 mM NH4NO3 were incapable of regaining nitrogenase activity, whereas control cultures returned to 65 to 80% of their original activity within about 3 h after exposure to high oxygen tension. In contrast to the regulation of heterocyst differentiation and nitrogenase synthesis, recovery from oxygen inactivation in this organism was shown to be under the control of NH4+ rather than NO3-.

Topics: Ammonium Chloride; Cyanobacteria; Kinetics; Nitrates; Nitrogenase; Oxygen; Quaternary Ammonium Compounds

Heterocysts were able to be induced while the blue-green alga Anabaena HA 101 were grown in a medium free from ammonium nitrate, but the heterocyst formation was inhibited while the Anabaena were grown in medium containing 5 mM ammonium nitrate. Heterocysts which had already formed were enhanced to senescence by the ammonium nitrate. Heterocyst transformation from certain vegetative cells into adult heterocysts accompanied with protein synthesis. A maximal level of protein synthesis as well as the high activity of nitrogenase was detected while the late proheterocysts transformed to mature heterocysts. Heterocyst is the site of nitrogenase synthesis and of the nitrogen fixation.

Topics: Culture Media; Cyanobacteria; Nitrates; Nitrogen Fixation; Nitrogenase; Plant Proteins