May bind free porphyrinogens that may be present in the cell and thus facilitate removal of these potentially toxic compound. Binds with a high affinity to one molecule of heme or porphyrins. It binds metalloporphyrins, free porphyrins and N-methylprotoporphyrin with similar affinities. Monomer. Forms a distorted beta-barrel structure, with two helices that are packed against the outer surface of the barrel. Porphyrins are expected to bind to a hydrophobic patch on the outer surface of the beta-barrel structure (By similarity). Belongs to the HEBP family.