Anaerobic transformation of coproporphyrinogen III into protoporphyrinogen IX. Dedicated to bacteriochlorophyll biosynthesis. coproporphyrinogen III + 2 S-adenosyl-L-methionine = 2 5'-deoxyadenosine + 2 CO2 + 2 L-methionine + protoporphyrinogen IX Binds 1 [4Fe-4S] cluster. The cluster is coordinated with 3 cysteines and an exchangeable S-adenosyl-L-methionine. Porphyrin-containing compound metabolism; protoporphyrin-IX biosynthesis; protoporphyrinogen-IX from coproporphyrinogen-III (AdoMet route): step 1/1. Monomer. Belongs to the anaerobic coproporphyrinogen-III oxidase family.