5VPN:
reference: Structural and biochemical analyses reveal insights into covalent flavinylation of the Escherichia coli Complex II homolog quinol:fumarate reductase., Starbird CA, Maklashina E, Sharma P, Qualls-Histed S, Cecchini G, Iverson TM, J Biol Chem. 2017 Jun 14. pii: jbc.M117.795120. doi: 10.1074/jbc.M117.795120. PMID: 28615448

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