4NTK:
reference: Biochemical and Structural Studies of 6-Carboxy-5,6,7,8-tetrahydropterin Synthase Reveal the Molecular Basis of Catalytic Promiscuity within the Tunnel-fold Superfamily., Miles ZD, Roberts SA, McCarty RM, Bandarian V, J Biol Chem. 2014 Aug 22;289(34):23641-52. doi: 10.1074/jbc.M114.555680. Epub, 2014 Jul 2. PMID: 24990950

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