protoporphyrinogen IX + 3 a quinone <=> protoporphyrin IX + 3 a quinol
protoporphyrinogen ix + 3 a quinone <=> protoporphyrin ix + 3 a quinol
protoporphyrinogen IX + 3 a quinone <=> protoporphyrin IX + 3 a quinol
protoporphyrinogen ix + 3 a quinone <=> protoporphyrin ix + 3 a quinol