Cytochrome b

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Mitochondrialny cytochrom bc1

Cytochrome b / b6 - major subunit of transmembrane cytochrome bc1 and b6f complexes. Cytochrome b is one of three catalytic subunits (in addition to cytochrome c1 and Rieski protein), found in mitochondria of eukaryotes and aerobic bacteria, ubichinol-cytochrome c oxidase, also known as complex III or cytochrome bc1 - depending on the organism.

A similar function in chloroplasts of plants and cyanobacteria is the cytochrome b6 cytochrome analogue, which is part of the cytochrome b6f complex. Struktura Citadel b is made up of 8 inner membrane helices. It contains two cofactors - hems b (high potential heme bH and low potential heme bL) that are non-covalently bound to the protein. Ligands for both hemis are four conserved histidine residues (two for each cofactor). Citochrome b contains a quinone reduction site (Qi site), which is located on the negative side of the membrane and coincides with the Rieski protein, the site of oxidation of hydroquinones (Qo site).

In cytochrome b6f, two subunits, cytochrome b6 and subunit IV are located in the cytochrome b site. Citron b6 is made up of four intramuscular helices and has a similar function as cytochrome b. It contains an additional cofactor, hem c, covalently attached by one conservative cysteine ​​residue. The extra cofactor function is not known, and is most likely involved in the cyclic phase of bright photosynthesis. Function

The main function of cytochrome b / b6 is the transfer of electrons between Qo and Qi. The same cytochrome b / b6 is responsible for the action of the proton pump, which generates a proton gradient. Transfer of electron from hydroquinone to heme BL is possible thanks to the movement of the Rieski protein domain containing iron-sulfur center. Then the electron moves to bH where it can be used to reduce quinones to semi- inin in Qi. In the next cycle, semichinon is reduced to hydroquinone and goes to the membrane.

The process of quinone reduction and electron transfer in cytochrome b / b6 is reversible.

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