Cytochromes

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Structure of the protein cytochrome  c with the prosthetic group heme  c

Cytochromes (also: cytochrome , from the Greek kýtos = vessel, cavity, cell and chroma = color ) are colored proteins (chromoproteins) (hence the name, which means "cell pigment") that contain heme as a prosthetic group and act as a redox mediator , as the iron ion in the heme changes its oxidation number . Cytochromes are differentiated according to the variant of the heme they contain and according to their light absorption spectrum .

They play a role in cell respiration , photosynthesis and other biochemical processes, where they act as carriers of electrons in redox reactions (cofactor of oxidoreductases ). There are around 50 different types. Cytochromes are found in cell organelles such as mitochondria and chloroplasts . In addition, cytochromes are found in animals in brown adipose tissue . The cytochromes - together with numerous vessels - give the fatty tissue its brown color.

history

The cytochromes were discovered by McMunn in 1884. It was only 40 years after the discovery that David Keilin was able to interpret the spectra of living cells as those of the three most important cytochromes a , b and  c .

properties

Cytochromes have one or more heme molecules as a prosthetic group . The cytochromes differ in the heme type and the apoprotein that surrounds the heme. Cytochromes a , b , c and d are differentiated according to their characteristic light absorption spectra .

Examples

The best-studied cytochrome is cytochrome c , which is obtained from the heart muscle tissue of tuna or horses . It consists of approximately 100 amino acids and the molecular structure is well characterized by protein crystallography . Cytochrome c is a very old protein in evolutionary terms .

In contrast to many other cytochromes that carry out tasks in electron transport, “ cytochrome P450 ” proteins and cyclooxygenases are enzymes , mostly oxygenases .

literature

  1. ↑ MeSH: Cytochromes
  2. ↑ Audrey Ensminger (Ed.): Foods & Nutrition Encyclopedia. Edition: 2, CRC Press, 1994, p. 1638. ISBN 0-8493-8980-1
  3. ↑ McMunn, C. A. (1884): On myohaematin, an intrinsic muscle-pigment of vertebrates and invertebrates, on histohaematin, and on the spectrum of the suprarenal bodies . In: Proceedings of the Physiological Society . Vol. 5, pp. XXIV-XXVI, PMC 1485163 (free full text).
  4. ↑ Keilin, D. (1925): On cytochrome, a respiratory pigment, common to animals, yeast, and higher plants . In: Proceedings of the Royal Society of London . Series B. Vol. 98, pp. 312-339 JSTOR 81121 .
  5. ↑ Margoliash, E. & Schejter, A (1984): 100 and 70 years ago: Myohaematins and histohaematins (cytochromes) . In: Trends Biochem. Sci. Vol. 9, pp. 364-367, doi: 10.1016 / 0968-0004 (84) 90062-8 .
  6. ^ Slater, EC (2003): Keilin, cytochrome, and the respiratory chain . In: J. Biol. Chem. Vol. 278, pp. 16455-16461. PMID 12560322 , doi: 10.1074 / jbc.X200011200 .

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