1FCJ:
reference: Identification of an allosteric anion-binding site on O-acetylserine sulfhydrylase: structure of the enzyme with chloride bound., Burkhard P, Tai CH, Jansonius JN, Cook PF, J Mol Biol 2000 Oct 20;303(2):279-86. PMID: 11023792

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