Myxothiazol is an inhibitor

Enzyme inhibitor

An enzyme inhibitor is a molecule that binds to enzymes and decreases their activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors. They are also used as herbicides and pesticides...

 of the mitochondrial cytochrome bc1 complex (coenzyme Q - cytochrome c reductase

Coenzyme Q - cytochrome c reductase

In enzymology, a ubiquinol—cytochrome-c reductase is an enzyme that catalyzes the chemical reactionThus, the two substrates of this enzyme are dihydroquinone and ferri- cytochrome c, whereas its 3 products are quinone , ferro- cytochrome c, and H+.This enzyme belongs to the family of...

).

Myxothiazol is a competitive inhibitor of ubiquinol

Ubiquinol

Ubiquinol is an electron-rich form of coenzyme Q10.The natural ubiquinol form of coenzyme Q10 is 2,3-dimethoxy-5-methyl-6-poly prenyl-1,4-benzoquinol, where the polyprenylated side chain is 9-10 units long in mammals...

, and binds at the quinol oxidation (Qo) site of the bc1 complex, blocking electron transfer to the Rieske iron-sulfur protein. Binding of myxothiazol induces a red-shift to the visible absorption spectrum of reduced haem bl. In contrast to stigmatellin

Stigmatellin

Stigmatellin is a potent inhibitor of the quinol oxidation site of the cytochrome bc1 complex in mitochondria and the cytochrome b6f complex of thylakoid membranes....

, myxothiazol does not form a hydrogen bond

Hydrogen bond

A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...

 to the Rieske iron-sulfur protein, binding instead in the 'b-proximal' region of the cytochrome b

Cytochrome b

Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...

Qo site. Movement of the cytoplasmic domain of the Rieske protein

Rieske protein

Rieske proteins are iron-sulfur protein components of cytochrome bc1 complexes and cytochrome b6f complexes which were first discovered and isolated by John S. Rieske and co-workers in 1964. It is a unique [2Fe-2S] cluster in that one of the two Fe atoms is coordinated by two histidine residues...

is therefore unaffected by the binding of this inhibitor.