Examples of three-dimensional structure of multi-heme proteins and identification of heme-binding environment. (A) Cytochrome c nitrite reductase of Wolinella succinogenes (PDB chain: 1FS7A) with 5 heme b molecules; (B) Thioalkalivibrio nitratireducens cytochrome c nitrite reductase (PDB chain: 3F29A) with 8 heme c molecules; (C) globin domain of globin-coupled sensor in Geobacter sulfurreducens (PDB chain: 2W31A). The red sticks are axial ligands of the heme iron and the blue sticks represent other heme interacting residues. For better visualization, the neighboring heme residues in A and B are colored yellow and green respectively. The heme molecules are shown as spacefill. The images were generated using Pymol http://www.pymol.org.