2QG9:
reference: Comparison of two T-state structures of regulatory-chain mutants of Escherichia coli aspartate transcarbamoylase suggests that His20 and Asp19 modulate the response to heterotropic effectors., Stec B, Williams MK, Stieglitz KA, Kantrowitz ER, Acta Crystallogr D Biol Crystallogr. 2007 Dec;63(Pt 12):1243-53. Epub 2007, Nov 16. PMID: 18084072

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).