2ZLB:
reference: Crystal structures of the Apo and Holo form of rat catechol-O-methyltransferase., Tsuji E, Okazaki K, Isaji M, Takeda K, J Struct Biol. 2008 Dec 10. PMID: 19111934

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