1ZDS:
reference: A rearranging ligand enables allosteric control of catalytic activity in copper-containing nitrite reductase., Wijma HJ, Macpherson I, Alexandre M, Diederix RE, Canters GW, Murphy ME, Verbeet MP, J Mol Biol. 2006 May 12;358(4):1081-93. Epub 2006 Mar 6. PMID: 16574144

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