fotosünteesi elektrontransportahela tsütokroom b6f kompleksis ja hingamisahela tsütokroom bc1 kompleksis esinev valguline alaühik, milles kaks raua aatomit on seotud kahe väävli aatomi abil kahe histidiini ja kahe tsüsteiini jäägiga, Rieske proteins are iron-sulfur protein (ISP) components of cytochrome bc1 complexes and cytochrome b6f complexes. It is a unique [2Fe-2S] cluster in that one of the two Fe atoms is coordinated by two histidine residues rather than two cysteine residues.