Figure 2.

Surface representation of the active site of the MPO monomer. PDB numbers: 3F9P, the light chain is shown in pink, and the heavy chain is shown in blue. There are 3 linkages between the heme and protein through Asp⁹⁴ on the light chain and Glu²⁴² and Met²⁴³ on the heavy chain (highlighted as yellow). The catalytically essential residues Gln⁹¹, His⁹⁵, and Arg²³⁹ (highlighted as red) compose the distal heme pocket; in the proximal site, the heme iron is coordinated through the His³³⁶ imidazole residue (highlighted as turquoise).