Protoporphyrinogen (IX) formation in heme synthesis
Seemingly the enzyme uses molecular oxygen in the reaction and one of the end products is water.

This reaction scheme is more detailed and presumably accurate.

http://www.hmdb.ca/reactions/3063

In addition there is also a set of papers detailing coproporphyrinogen oxidase which was also on the website, hopefully one goes into more detail on the reaction.

http://www.hmdb.ca/proteins/HMDBP00251