3HRD:
reference: The Mo-Se active site of nicotinate dehydrogenase., Wagener N, Pierik AJ, Ibdah A, Hille R, Dobbek H, Proc Natl Acad Sci U S A. 2009 Jul 7;106(27):11055-60. Epub 2009 Jun 22. PMID: 19549881

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