Allows bacterial pathogens to use the host heme as an iron source. Catalyzes the oxidative degradation of the heme macrocyclic porphyrin ring to the oxo-bilirubin chromophore staphylobilin (a mixture of the linear tetrapyrroles 5-oxo-delta-bilirubin and 15-oxo-beta-bilirubin) in the presence of a suitable electron donor such as ascorbate or NADPH--cytochrome P450 reductase, with subsequent release of free iron. 5 AH2 + 2 H(+) + heme b + 4 O2 = 5 A + delta-staphylobilin + Fe(2+) + formaldehyde + 4 H2O 5 AH2 + 2 H(+) + heme b + 4 O2 = 5 A + beta-staphylobilin + Fe(2+) + formaldehyde + 4 H2O Homodimer. Regulated by iron in a Fur-dependent manner and by heme. Belongs to the antibiotic biosynthesis monooxygenase family. Heme-degrading monooxygenase IsdG subfamily.