Involved in coproporphyrin-dependent heme b biosynthesis (PubMed:7928957, PubMed:9217019). Catalyzes the oxidation of coproporphyrinogen III to coproporphyrin III (PubMed:8288631, PubMed:7928957, PubMed:9217019, PubMed:9784236). Can also oxidize protoporphyrinogen IX to protoporphyrin-IX (PubMed:8288631, PubMed:7928957, PubMed:9217019, PubMed:9784236, PubMed:19944166). The specific activity for the oxidation of coproporphyrinogen III is much higher than that for the oxidation of protoporphyrinogen IX (PubMed:7928957, PubMed:9217019). Can also oxidize mesoporphyrinogen IX, but not uroporphyrinogen III (PubMed:8288631, PubMed:9784236, PubMed:7928957). coproporphyrinogen III + 3 O2 = coproporphyrin III + 3 H2O2 Binds 1 FAD per subunit. Only weakly inhibited by acifluorfen, in contrast to eukaryotic family members (PubMed:8288631, PubMed:9784236, PubMed:19944166). Weakly inhibited by methylacifluorfen (PubMed:9784236). Bilirubin, biliverdin and hemin are all competitive inhibitors (PubMed:9784236). kcat is 0.05 min(-1) with coproporphyrinogen III as substrate (PubMed:9784236). kcat is 0.19 min(-1) with protoporphyrinogen IX as substrate (PubMed:9784236). kcat is 2.69 min(-1) with mesoporphyrinogen IX as substrate (PubMed:9784236). Optimum pH is 8.7 (for protoporphyrinogen oxidation). Porphyrin-containing compound metabolism; protoheme biosynthesis. Monomer. Mutations cause the accumulation of coproporphyrinogen III or coproporphyrin III in the growth medium and the accumulation of trace amounts of other porphyrinogens or porphyrins intracellularly. Belongs to the protoporphyrinogen/coproporphyrinogen oxidase family. Coproporphyrinogen III oxidase subfamily.