| The mitochondrial enzyme, coproporphyrinogen III oxidase,
catalyzes the next reaction.
- The substrate is coproporphyrinogen III.
- The reaction is conversion of the propionic acid groups of rings I and III to vinyl groups. We now have the final substituent pattern of MV MV MP PM (note that "Petrarchan" pattern of the last four substituent groups).
- The product is protoporphyrinogen IX (pronounce). (Some naming systems would call this protoporphyrinogen III to preserve the logic of the nomenclature, but "protoporphyrinogen III" is a departure from a time-honored tradition of referring to this and subsequent compounds by the number "IX.")