111 - Localization and activities of nitrogenase, glutamine synthetase and glutamate synthase in Azotobacter vinelandii grown in oxygen-controlled continuous culture

Previous research showed that A. vinelandii forms intracellular membrane structures in certain oxygen conditions (098). This could function to protect the sensitive nitrogenase from oxygen, except that one study seemed to disprove any such enzyme localization; this study was inadequate though.

So Röckel, Oelze and colleagues decided to test this hypothesis better, using oxygen-controlled continuous culture. They also tested localization of glutamine and glutamate synthases (which incorporate nitrogenase-fixed nitrogen into biomass).

What They Saw

First, the more oxygen saturation, the less nitrogenase activity (and protein content in general) they observed. In cell-free extracts, nitrogenase was only found in the soluble fraction (and thus wasn't membrane-bound). Glutamine synthase also seems all soluble.

With glutamate synthase, on the other hand, as oxygen increased, membrane-bound activity increased while soluble activity decreased.

What This Means

It's not impossible that the soluble-seeming enzymes may have a weak attachment to membranes that couldn't be resolved in this study, but it didn't seem like the membranes affected them much. The increase in membrane-bound glutamate synthase might be a form of stabilization with increasing oxygen.

Reference:

Röckel, D., Hernando, J. J., Vakalopoulou, E., Post, E. & Oelze, J. Localization and activities of nitrogenase, glutamine synthetase and glutamate synthase in Azotobacter vinelandii grown in oxygen-controlled continuous culture. Archives of Microbiology 136, 74–78 (1983).