What They Saw
They detected only Mo, no V, in the preparation. The activities they saw were pretty weird in some ways: the electron flux going to nitrogen was almost as much as in the Mo nitrogenase (~70%, with the rest going to hydrogen), whereas with the normal FeVco, 50% went to each; in previous studies, V nitrogenase with FeMoco couldn't fix nitrogen at all. On the other hand, with acetylene, almost all electrons went to ethylene in the Mo nitrogenase, whereas only 30-35% did in the V nitrogenase with either cofactor, while 3% went to ethane with FeVco but 10% did with FeMoco, which is consistent with previous studies. So I'm confused.
When they added carbon monoxide, there was inhibition of all nitrogenase versions, as expected.
What This Means
I think something was weird in this study, but I don't know what. It seems very questionable. However, most of the later studies citing this one either accept it without question, or confirm its results, so maybe it's not as questionable as it seems.
Also, it's worth noting that the results only show the electron flux going to each substrate, not the total electron flux, so even if most electrons go to nitrogen in the FeMoco-substituted V nitrogenase, it's still possible that it's fixing a lot less nitrogen overall than either Mo or V versions proper.