Figure 3.

P. aeruginosa has two heme uptake systems, Phu, and Has. The PhuR TonB-dependent receptor binds directly hemoproteins extracting heme while the HasR receptor binds heme complexed to a secreted hemophore protein HasA. In the periplasm heme is bound to a periplasmic protein which delivers it to an ABC transporter. In the cytoplasm heme is directed to the heme oxygenase HemO by the PhuS chaperone. HemO cleaves the tetrapyrrole ring, leaving biliverdin, CO, and Fe²⁺.