Friday, May 22, 2015

197 - Superoxide dismutase and catalase in Azotobacter vinelandii grown in continuous culture at different dissolved oxygen concentrations

Considering how oxygen-sensitive nitrogenase is, it might be expected that enzymes specifically involved in oxygen detoxification (such as catalase and superoxide dismutase (SOD)) might be involved in protecting such oxygen-sensitive enzymes, especially since ramping up respiration in response to increased oxygen might also ramp up the production of reactive oxygen species. This study investigates the activity of SOD and catalase in Azotobacter vinelandii at different oxygen levels.

What They Saw
They grew A. vinelandii OP (aka CA) in chemostats with different levels of oxygen, with 3 or 15 g/L sucrose. They extracted enzymes from samples and assayed them for SOD or catalase activity, and also by electrophoresis.

As oxygen saturation increased from 1% to 90%, SOD activity increased linearly (when standardized to total protein); the increase was slightly faster at lower oxygen when standardized by number of cells (probably because cell size increases as oxygen increases, 098). The sucrose concentration didn't affect things. When cells were given ammonia, SOD activity was about 2x lower.

Based on electrophoresis, they concluded that the SOD is iron-containing, rather than manganese. They tried adding manganese but still didn't see any Mn-SOD.

It didn't seem like catalase activity increased with increasing oxygen, standardized by protein. The increase standardized by cells was much more apparent.

What This Means
It seems like SOD at least might contribute to A. vinelandii's protection of its nitrogenase enzyme from oxygen.


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