4HPP:
reference: Structure and Activity of PA5508, a Hexameric Glutamine Synthetase Homologue., Ladner JE, Atanasova V, Dolezelova Z, Parsons JF, Biochemistry. 2012 Dec 21;51(51):10121-3. doi: 10.1021/bi3014856. Epub 2012 Dec, 12. PMID: 23234431

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