1HVA:
reference: Engineering the zinc binding site of human carbonic anhydrase II: structure of the His-94-->Cys apoenzyme in a new crystalline form., Alexander RS, Kiefer LL, Fierke CA, Christianson DW, Biochemistry 1993 Feb 16;32(6):1510-8. PMID: 8431430

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