1PV8:
reference: Control of tetrapyrrole biosynthesis by alternate quaternary forms of porphobilinogen synthase., Breinig S, Kervinen J, Stith L, Wasson AS, Fairman R, Wlodawer A, Zdanov A, Jaffe EK, Nat Struct Biol 2003 Sep;10(9):757-63. Epub 2003 Aug 3. PMID: 12897770

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