At higher concentrations, stigmatellin also inhibits Complex I, as a "Class B" inhibitor of that enzyme.

[2] Stigmatellin is isolated from the myxobacterium Stigmatella aurantica, and contains a 5,7-dimethoxy-8-hydroxychromone aromatic headgroup with a hydrophobic alkenyl chain in position 2.

Crystal structures for stigmatellin-inhibited bc1 complex from bovine, avian, yeast (Saccharomyces cerevisiae) and bacterial (Rhodobacter capsulatus, Cereibacter sphaeroides, and Paracoccus denitrificans) sources are available.

Stigmatellin binds at the cytochrome b Qo site in the '(heme) bl distal' position, and associates with the Rieske iron-sulfur protein via a hydrogen bond to histidine residue 181 (His-181), a ligand to the [2Fe2S] iron-sulfur cluster of this subunit.

This association raises the midpoint potential of the iron-sulfur cluster from 290 to 540 mV and restricts movement of the cytoplasmic domain of the Rieske protein.