3T8N:
reference: Evaluating the Catalytic Contribution from the Oxyanion Hole in Ketosteroid Isomerase., Schwans JP, Sunden F, Gonzalez A, Tsai Y, Herschlag D, J Am Chem Soc. 2011 Nov 4. PMID: 22053826

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