obsolete protoporphyrinogen IX metabolic process https://github.com/geneontology/go-ontology/issues/31788 true This term was obsoleted because protoporphyrinogen IX is an intermediate in heme/chlorophyll/uroporphyrinogen biosynthesis. protoporphyrinogen IX metabolism GO:0046501 biological_process OBSOLETE. The chemical reactions and pathways involving protoporphyrinogen IX, the specific substrate for the enzyme ferrochelatase, which catalyzes the insertion of iron to form protoheme. It is probably also the substrate for chlorophyll formation.