5YLY:
reference: Structural and enzymatic analysis of the cytochrome b5 reductase domain of Ulva prolifera nitrate reductase., You C, Liu C, Li Y, Jiang P, Ma Q, Int J Biol Macromol. 2018 May;111:1175-1182. doi: 10.1016/j.ijbiomac.2018.01.140., Epub 2018 Feb 19. PMID: 29371148

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