Involved in coproporphyrin-dependent heme b biosynthesis (PubMed:26083961). Catalyzes the decarboxylation of Fe-coproporphyrin III (coproheme) to heme b (protoheme IX), the last step of the pathway (PubMed:26083961, PubMed:27936663, PubMed:27982566). The reaction occurs in a stepwise manner with a three-propionate harderoheme intermediate (PubMed:26083961, PubMed:27936663, PubMed:27982566). The first decarboxylation step is fast and yields the three-propionate harderoheme isomer III intermediate, while the slower second decarboxylation appears to control the overall rate. H(2)O(2) is the assumed biological oxidant, but either H(2)O(2) or peracetic acid yields the same intermediates and products (PubMed:26083961). Has weak peroxidase and catalase activities in vitro (PubMed:23737523). Fe-coproporphyrin III + 2 H(+) + 2 H2O2 = 2 CO2 + 4 H2O + heme b Fe-coproporphyrin III + H(+) + H2O2 = CO2 + 2 H2O + harderoheme III H(+) + H2O2 + harderoheme III = CO2 + 2 H2O + heme b Fe-coproporphyrin III acts as both substrate and redox cofactor (Probable). Was originally thought to use heme as a cofactor (PubMed:23737523). Porphyrin-containing compound metabolism; protoheme biosynthesis. Homohexamer. Deletion mutant forms slow growing small colonies under aerobic but not anaerobic conditions. Mutant accumulates coproporphyrin specifically under aerobic conditions and shows deficiencies in catalase activity and peroxide resistance. Belongs to the ChdC family. Type 1 subfamily.