Identification of HBPs. (A) Hemin binding blot. M, prestained molecular mass standard (Peqlab, Germany); lane 1, cytoplasmic and inner membrane proteins; lane 2, outer membrane proteins. (B) Hemin-agarose binding assay (silver stained). M, prestained molecular mass standard (Bio-Rad); lane 1, outer membrane proteins; lanes 2 to 4, purification steps: lane 2, supernatant after incubation with hemin-agarose; lane 3, supernatant after washing in high-salt buffer; lane 4, supernatant after washing in low-salt buffer; lane 5, HBPs. The major HBPs of 89, 80, 43, 34, and 31 kDa are marked by asterisks.