What They Saw
They were unable to get pure, soluble enzyme; they couldn't separate it from the membrane, so it remained in insoluble particles.
They observed that hydrogenase activity of these particles didn't decrease after 18 days of exposure to air, unlike particles from other species. They did lose activity within a few weeks though.
They also observed that the enzyme reduces cytochrome C, possibly as part of its electron transport role. They found that carbon monoxide and cyanide inhibit the enzyme. Azide does not, at least not at pH 8.
What This Means
Some of the observations here may be due to the presence of other membrane-bound proteins, not just hydrogenase.