1FON:
reference: Crystal structure of bovine procarboxypeptidase A-S6 subunit III, a highly structured truncated zymogen E., Pignol D, Gaboriaud C, Michon T, Kerfelec B, Chapus C, Fontecilla-Camps JC, EMBO J 1994 Apr 15;13(8):1763-71. PMID: 8168476

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