1XQE:
reference: The mechanism of ammonia transport based on the crystal structure of AmtB of Escherichia coli., Zheng L, Kostrewa D, Berneche S, Winkler FK, Li XD, Proc Natl Acad Sci U S A 2004 Dec 7;101(49):17090-5. Epub 2004 Nov 24. PMID: 15563598

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