3IPT:
reference: Dissecting the paradoxical effects of hydrogen bond mutations in the ketosteroid isomerase oxyanion hole., Kraut DA, Sigala PA, Fenn TD, Herschlag D, Proc Natl Acad Sci U S A. 2010 Feb 2;107(5):1960-5. Epub 2010 Jan 11. PMID: 20080683

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