The two long central helices cross at the active site; both helices include internal stretches of π-helix that provide three histidine (His) ligands to the active site iron.
As dúas longas hélices centrais cruzan no sitio activo; ambas as hélices inclúen tramos internos de hélice π que proporcionan tres ligandos histidina (His) ao ferro do sitio activo.