1I90:
reference: Structural aspects of isozyme selectivity in the binding of inhibitors to carbonic anhydrases II and IV., Kim CY, Whittington DA, Chang JS, Liao J, May JA, Christianson DW, J Med Chem 2002 Feb 14;45(4):888-93. PMID: 11831900

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