4CTR:
reference: Nitric Oxide Synthase Inhibitors that Interact with both a Heme Propionate and Tetrahydrobiopterin Show High Isoform Selectivity., Kang S, Tang W, Li H, Chreifi G, Martasek P, Roman LJ, Poulos TL, Silverman RB, J Med Chem. 2014 Apr 23. PMID: 24758147

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