1.8.99.5	Cu	the heterobimetallic active-site heme 2 has a Cu(I) ion juxtaposed to a heme c at a Fe-Cu distance of 4.4 A. While the combination of metals is reminiscent of respiratory heme–copper oxidases, the oxidation-labile Cu(I) centre of MccA does not seem to undergo a redox transition during catalysis. The copper-depleted form II of MccA, the absence of the heterometal allows for a binding mode of sulfite that is similar to the one seen in the siroheme-containing enzymes or in NrfA. In the structure of the Cu-containing, high-activity form I of MccA, all 12 monomers in the asymmetric unit have a ligand bound to heme 2	743347	
1.8.99.5	Fe	the heterobimetallic active-site heme 2 has a Cu(I) ion juxtaposed to a heme c at a Fe-Cu distance of 4.4 A	743347	
1.8.99.5	Iron	20 mol of iron per mol of enzyme	733765	
1.8.99.5	Iron	20 to 21 nonheme iron atoms per enzyme molecule	394043	
1.8.99.5	Iron	24 mol of iron per mol of enzyme	394066	
1.8.99.5	Iron	contains 22 non-heme iron atoms per molecule	734637