1RGZ:
reference: Hydrolysis of third-generation cephalosporins by class C beta-lactamases. Structures of a transition state analog of cefotoxamine in wild-type and extended spectrum enzymes., Nukaga M, Kumar S, Nukaga K, Pratt RF, Knox JR, J Biol Chem 2004 Mar 5;279(10):9344-52. Epub 2003 Dec 3. PMID: 14660590

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