1FXU:
reference: Calf spleen purine nucleoside phosphorylase: structure of its ternary complex with an N(7)-acycloguanosine inhibitor and a phosphate anion., Luic M, Koellner G, Shugar D, Saenger W, Bzowska A, Acta Crystallogr D Biol Crystallogr 2001 Jan;57(Pt 1):30-6. PMID: 11134924

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