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.")