1GGU: Human Factor Xiii With Calcium Bound In The Ion Site
reference: Identification of the calcium binding site and a novel ytterbium site in blood coagulation factor XIII by x-ray crystallography., Fox BA, Yee VC, Pedersen LC, Le Trong I, Bishop PD, Stenkamp RE, Teller DC, J Biol Chem 1999 Feb 19;274(8):4917-23. PMID: 9988734

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