Page "Oxidative phosphorylation" Paragraph 12

Within proteins, electrons are transferred between flavin cofactors, iron – sulfur clusters, and cytochromes.

There are several types of iron – sulfur cluster.

The simplest kind found in the electron transfer chain consists of two iron atoms joined by two atoms of inorganic sulfur ; these are called clusters.

The second kind, called, contains a cube of four iron atoms and four sulfur atoms.

Each iron atom in these clusters is coordinated by an additional amino acid, usually by the sulfur atom of cysteine.

Metal ion cofactors undergo redox reactions without binding or releasing protons, so in the electron transport chain they serve solely to transport electrons through proteins.

Electrons move quite long distances through proteins by hopping along chains of these cofactors.

This occurs by quantum tunnelling, which is rapid over distances of less than 1. 4 m.