The heme acquisition systemA protein secreted by Pseudomonas aeruginosa (HasA(p)) can capture several synthetic metal complexes other than heme. The crystal structures of HasA(p) harboring synthetic metal complexes revealed only small perturbation of the overall HasA(p) structure. An inhibitory effect upon heme acquisition by HasA(p) bearing synthetic metal complexes was examined by monitoring the growth of Pseudomonas aeruginosa PAO1. HasA(p) bound to iron-phthalocyanine inhibits heme acquisition in the presence of heme-bound HasA(p) as an iron source.