4U4V:
reference: Structural basis for dynamic mechanism of nitrate/nitrite antiport by NarK., Fukuda M, Takeda H, Kato HE, Doki S, Ito K, Maturana AD, Ishitani R, Nureki O, Nat Commun. 2015 May 11;6:7097. doi: 10.1038/ncomms8097. PMID: 25959928

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