Involved in coproporphyrin-dependent heme b biosynthesis. Catalyzes the oxidation of coproporphyrinogen III to coproporphyrin III. coproporphyrinogen III + 3 O2 = coproporphyrin III + 3 H2O2 Binds 1 FAD per subunit. Porphyrin-containing compound metabolism; protoheme biosynthesis. Belongs to the protoporphyrinogen/coproporphyrinogen oxidase family. Coproporphyrinogen III oxidase subfamily.