Wednesday, August 12, 2015

558 - Isolation of a new vanadium-containing nitrogenase from Azotobacter vinelandii

This study is the first to fully purify the vanadium nitrogenase from Azotobacter vinelandii.

What They Saw
They used strain UW (aka CA) and a nifHDK knockout. It didn't seem like they scrubbed the medium for Mo, but they did test the purified product for metals and didn't see a detectable amount of Mo, only V and Fe (in a 1-to-13 ratio), so I guess it's good.

They did acetylene reduction assays on the V and Mo nitrogenases, and found that 90% of the electrons went to acetylene in the former, but only 12% in the latter. It seems like they only measured ethylene production though, so they might've underestimated the total activity by neglecting the ethane produced by the V nitrogenase.

Under argon, the Mo nitrogenase produced 1.6x more hydrogen than the V version. This was the same ratio as that of nitrogen fixed by each version. I'm not sure how much it's possible to compare these enzymes in vitro though. But it seems like the V nitrogenase is better at nitrogen and hydrogen than at acetylene.

As mentioned, ICP emission spectroscopy didn't detect any metals other than V or Fe: no Mo, Cr, Co, Ni, Cu, or W, so that's good.

What This Means
This shows how the Mo and V nitrogenases are similar in some ways and yet different in others. They work in similar ways and are sensitive to similar things, but the products of their reactions and such are different (though possible substrates seem largely the same). By comparing the two, we can learn more about the process of nitrogen fixation in general.

Hales, B. J., Case, E. E., Morningstar, J. E., Dzeda, M. F. & Mauterer, L. A. Isolation of a new vanadium-containing nitrogenase from Azotobacter vinelandii. Biochemistry 25, 7251–7255 (1986).

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