Catalyzes the 6-electron oxidation of protoporphyrinogen-IX to form protoporphyrin-IX. Provides precursor for the mitochondrial and plastidic heme synthesis and the predominant chlorophyll synthesis in plastids. 3 O2 + protoporphyrinogen IX = 3 H2O2 + protoporphyrin IX Binds 1 FAD per subunit. Inhibited by the herbicide acifluorfen. Porphyrin-containing compound metabolism; protoporphyrin-IX biosynthesis; protoporphyrin-IX from protoporphyrinogen-IX: step 1/1. Expressed in expanding premature leaves. Decreased expression in oldest leaves. Also detected in roots. Oscillating expression during diurnal growth. Maximal expression in the dark period. Belongs to the protoporphyrinogen/coproporphyrinogen oxidase family. Protoporphyrinogen oxidase subfamily.