1FIQ:
reference: Crystal structures of bovine milk xanthine dehydrogenase and xanthine oxidase: structure-based mechanism of conversion., Enroth C, Eger BT, Okamoto K, Nishino T, Nishino T, Pai EF, Proc Natl Acad Sci U S A 2000 Sep 26;97(20):10723-8. PMID: 11005854

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