Involved in coproporphyrin-dependent heme b biosynthesis (PubMed:25908396). Catalyzes the oxidation of coproporphyrinogen III to coproporphyrin III (PubMed:25908396, PubMed:27597779). Can also oxidize protoporphyrinogen IX (PubMed:27597779). coproporphyrinogen III + 3 O2 = coproporphyrin III + 3 H2O2 Binds 1 FAD per subunit. The generation of protoporphyrin IX, but not coproporphyrin III, is stimulated by heme-bound HemQ. This stimulatory effect is mediated by superoxide (PubMed:27597779). Inhibited by acifluorfen analogs (PubMed:25908396). kcat is 1.33 min(-1) with coproporphyrinogen III as substrate (PubMed:25908396). kcat is 0.46 min(-1) with coproporphyrinogen III as substrate (PubMed:27597779). kcat is 0.44 min(-1) with protoporphyrinogen IX as substrate (PubMed:27597779). Porphyrin-containing compound metabolism; protoheme biosynthesis. Belongs to the protoporphyrinogen/coproporphyrinogen oxidase family. Coproporphyrinogen III oxidase subfamily.