Oxygen protection of nitrogenase in the aerobically nitrogen fixing, non-heterocystous cyanobacteriumOscillatoriasp.

✍ Scribed by Lucas J. Stal; Wolfgang E. Krumbein

• Publisher: Springer
• Year: 1985
• Tongue: English
• Weight: 549 KB
• Volume: 143
• Category: Article
• ISSN: 0302-8933
• DOI: 10.1007/bf00414771

✦ Synopsis

Oscillatoria sp. strain 23 is a filamentous, nonheterocystous cyanobacterium that fixes nitrogen aerobically. Although, in this organism nitrogenase is inactivated by oxygen a high tolerance is observed. Up to a pO2 of 0.15 atm, oxygen does not have any measurable effects on acetylene reduction. Higher concentrations of oxygen inhibited the activity to a relatively high degree. Evidence for two mechanisms of oxygen protection of nitrogenase in this cyanobacterium was obtained. A high rate of synthesis of nitrogenase may allow the organism to maintain a certain amount of active enzyme under aerobic conditions. Secondly, a switch off/on mechanism may reversibly convert the active enzyme into a non-active form which is insensitive to oxygen inactivation after a sudden and short-term exposure to high oxygen concentrations. It is conceived that these mechanisms in addition to a temporal separation of nitrogen fixation from oxygenic photosynthesis sufficiently explain the regulation process of aerobic nitrogen fixation in this organism,