1AXJ:
reference: Pathway of chymotrypsin evolution suggested by the structure of the FMN-binding protein from Desulfovibrio vulgaris (Miyazaki F), Liepinsh E, Kitamura M, Murakami T, Nakaya T, Otting G, Nat Struct Biol 1997 Dec;4(12):975-9. PMID: 9406543

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