Involved in the heme biosynthesis. Catalyzes the aerobic oxidative decarboxylation of propionate groups of rings A and B of coproporphyrinogen-III to yield the vinyl groups in protoporphyrinogen-IX. coproporphyrinogen III + 2 H(+) + O2 = 2 CO2 + 2 H2O + protoporphyrinogen IX Porphyrin-containing compound metabolism; protoporphyrin-IX biosynthesis; protoporphyrinogen-IX from coproporphyrinogen-III (O2 route): step 1/1. Homodimer. Belongs to the aerobic coproporphyrinogen-III oxidase family.