Respiration redox changes, cytochromes

The first of these new, electron transferring components was coenzyme Q (CoQ). Festenstein in R.A. Morton s laboratory in Liverpool had isolated crude preparations from intestinal mucosa in 1955. Purer material was obtained the next year from rat liver by Morton. The material was lipid soluble, widely distributed, and had the properties of a quinone and so was initially called ubiquinone. Its function was unclear. At the same time Crane, Hatefi and Lester in Wisconsin were trying to identify the substances in the electron transport chain acting between NADH and cytochrome b. Using lipid extractants they isolated a new quininoid coenzyme which showed redox changes in respiration. They called it coenzyme Q (CoQ). CoQ was later shown to be identical to ubiquinone. 

Cytochrome c has a number of vital functions inside the cell. As part of the mitochondrial electron transport chain in respiration, it shuttles redox equivalents to cytochrome c oxidase (28), which can be considered as a kind of natural fuel cell for energy conversion. Mitochondrial dysfunction accompanied with changes in cytochrome c oxidase activity, however, seems to be intimately related to aging, neurodegeneration, and disease (29). Effects that can manipulate the fimctions of such redox enz5unes are therefore of great importance for many research fields. 

Electron transport is by virtue of a reversible valency change of the inorganic heme iron the main biological function of the cytochromes in various biological redox reactions (e.g. respiration, photosynthesis). The porphyrin ligand can always participate in the sequence of reactions. 

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