1QK5:
reference: Crystal structure of Toxoplasma gondii hypoxanthine-guanine phosphoribosyltransferase with XMP, pyrophosphate, and two Mg(2+) ions bound: insights into the catalytic mechanism., Heroux A, White EL, Ross LJ, Davis RL, Borhani DW, Biochemistry 1999 Nov 2;38(44):14495-506. PMID: 10545171

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