query: has_part protoporphyrinogen ix
supports: Porphyrins are a group of heterocyclic macrocycle organic compounds, composed of four modified pyrrole subunits interconnected at their  carbon atoms via methine bridges (=CH). The parent porphyrin is porphin, and substituted porphines are called porphyrins. The porphyrin ring structure is aromatic, with a total of 26 electrons in the conjugated system. Various analyses indicate that not all atoms of the ring are involved equally in the conjugation or that the molecule's overall nature is substantially based on several smaller conjugated systems. One result of the large conjugated system is that porphyrin molecules typically have very intense absorption bands in the visible region and may be deeply colored; the name "porphyrin" comes from the Greek word  ("porphyra"), meaning "purple". Protoporphyrins are tetrapyrroles containing the following side chains:  Protoporphyrin IX is a biochemical widely used as a carrier molecule for divalent cations. Together with iron (Fe 2+) the body of the heme- group of hemoglobin, myoglobin and many other heme-containing enzymes like cytochrome c and catalase are formed. Complexed with magnesium-ions (Mg 2+) the main part of the Chlorophylls are formed. Complexed with zinc-ions (Zn 2+) it forms Zinc protoporphyrin. Protoporphyrinogen IX is a precursor for protoporphyrin IX. See Porphyrins for the pathway and more information . Protoporphyrin IX, in the metabolism of porphyrin, is created by the enzyme protoporphyrinogen oxidase.
candidates: a c carbon group metabolism s side system word zinc
answer: carbon