Illustration of the haemophore protein HasAp from the bacterium Pseudomonas aeruginosa complexed with the synthetic pseudo-haeme structure manganese tetraphenylporphyrin. P. aeruginosa uses respiratory enzymes that need iron or iron-containing cofactors for their function. Haemophores are excreted into the extracellular medium in low iron conditions to bind to haemoproteins and extract the haeme. They then bind receptors on the bacterial cell membrane that transport the haem into the cell.