has participant hydron carbon dioxide uroporphyrinogen III(8-) coproporphyrinogen III(4-) uroporphyrinogen decarboxylase activity RHEA:19865 MetaCyc:UROGENDECARBOX-RXN uroporphyrinogen III decarboxylase activity porphyrinogen decarboxylase activity porphyrinogen carboxy-lyase activity Catalysis of the reaction: uroporphyrinogen-III = coproporphyrinogen + 4 CO2. GO:0004853 EC:4.1.1.37 uroporphyrinogen-III carboxy-lyase (coproporphyrinogen-III-forming) uroporphyrinogen-III carboxy-lyase activity molecular_function carboxy-lyase activity