What They Saw
Hydrogen production depended on ATP. Argon or hydrogen in the atmosphere didn't matter. The higher the protein concentration, the more hydrogen was produced. At 0ºC in air, the enzyme was pretty stable; over 90% activity was left after 3 days.
Hydrogen oxidation activity was found in separate fractions from the production activity, so they concluded it was a different enzyme.
Comparing extracts from cells grown with urea or no fixed nitrogen, they saw no hydrogen production activity in urea samples, but the hydrogen oxidation activity with urea was lower than that without.
What This Means
We know now that the hydrogen production comes from nitrogenase and the hydrogen oxidation from hydrogenase. It's surprising how air-stable the nitrogenase seemed to be outside the context of the cell, but I guess it was still surrounded by cellular elements in the crude extract. Also I'm not sure how oxygen inactivation affects nitrogenase hydrogen production.