Catalyzes the oxidation of protoporphyrinogen IX to protoporphyrin IX. Is involved in the biosynthesis of tetrapyrrole molecules like heme and chlorophyll. Does not use oxygen or artificial electron acceptors such as menadione or benzoquinone. Is functionally coupled with coproporphyrinogen III oxidase (CPO) (PubMed:29925590). Is essential for growth (PubMed:20823222). 3 A + protoporphyrinogen IX = 3 AH2 + protoporphyrin IX Binds 1 heme b (iron(II)-protoporphyrin IX) group per subunit. Porphyrin-containing compound metabolism; protoporphyrin-IX biosynthesis; protoporphyrin-IX from protoporphyrinogen-IX: step 1/1. Homodimer. Can also form higher oligomers, most probably tetramers. Interacts with Sll1106, however it is unlikely that Sll1106 is required for PPO function. Attempts to disrupt this gene in the wild-type background of Synechocystis only allow to obtain heteroplasmic disruptants. These cells accumulate a substantial amount of protoporphyrin IX. Belongs to the HemJ family.