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 Inhibited by protoporphyrinogen-IX, by metal chelator (EGTA) and by low concentrations of heavy metal ions. kcat is 0.17 min(-1) for decarboxylation of coproporphyrinogen-III (at pH 6 and at 37 degrees Celsius). Optimum pH is between 6 and 7. 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.