In cell biology, microsomes are vesicle-like artifacts re-formed from pieces of the endoplasmic reticulum (ER) when eukaryotic cells are broken-up in the laboratory; by definition, microsomes are not ordinarily present in living cells.[1]

Microsomes can be concentrated and separated from other cellular debris by differential centrifugation. Unbroken cells, nuclei, and mitochondria sediment out at 10,000g, whereas soluble enzymes and fragmented ER, which contains cytochrome P450 (CYP), remain in solution (g is the Earth's gravitational acceleration). At 100,000g, achieved by faster centrifuge rotation, ER sediments out of solution as a pellet but the soluble enzymes remain in the supernatant. In this way, cytochrome P450 in microsomes is concentrated and isolated. Microsomes have a reddish brown color, due to the presence of the iron-containing co-factor, heme (haem), in the P450s. P450s are highly abundant in livers of rats, mice and humans.

Microsomes are a valuable tool for investigating the metabolism of compounds (enzyme inhibition, clearance and metabolite identification) and for examining drug-drug interactions by in vitro-research. Researchers often select microsome lots based on the enzyme activity level of specific CYPs. Some lots are available to study specific populations (example: lung microsomes from smokers or non-smokers) or divided into classifications to meet target CYP activity levels for inhibition and metabolism studies.

See also

  • S9 fraction (postmitochondrial fraction).
  • Antimicrosomal antibody


  1. ^ Voet, Donald; Voet, Judith G. (2004). Biochemistry (3rd ed.). Wiley. p. 1309. ISBN 0-471-19350-x. 

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Look at other dictionaries:

  • microsome — n. (Cell biology) a tiny granule in the cytoplasm of a cell; it consists of ribosomes bound to fragments of the endoplasmic reticulum and mitochondria. [WordNet 1.5 +PJC] …   The Collaborative International Dictionary of English

  • microsome — microsome. См. хромидия. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • microsome — [mī′krōsōm΄] n. [ MICRO + SOME3] any of a number of minute granules in the cytoplasm of an active cell, that are filled with enzymes and thought to be associated with protein synthesis microsomal adj …   English World dictionary

  • Microsome — Les microsomes sont des fragments de membranes du réticulum endoplasmique. Plus précisément, il s agit de vésicules provenant de la fragmentation du réticulum endoplasmique. Il existe deux sortes de microsomes : les microsomes rugueux… …   Wikipédia en Français

  • microsome — noun Etymology: International Scientific Vocabulary Date: 1885 1. any of various minute cellular structures (as a ribosome) 2. a particle in a particulate fraction that is obtained by heavy centrifugation of broken cells and consists of various… …   New Collegiate Dictionary

  • microsome — microsomal, microsomial, microsomic, adj. /muy kreuh sohm /, n. Cell Biol. a small inclusion, consisting of ribosomes and fragments of the endoplasmic reticulum and mitochondria, in the cytoplasm of a cell. [1880 85; MICRO + SOME3] * * * …   Universalium

  • microsome — noun /ˈmaɪk.rə.səʊm,ˈmaɪk.rə.soʊm/ A vesicle formed as an artifact of cell disruption …   Wiktionary

  • microsome — One of the small spherical vesicles derived from the endoplasmic reticulum after disruption of cells and ultracentrifugation. [micro + G. soma, body] * * * mi·cro·some mī krə .sōm n 1) any of various minute cellular structures (as a ribosome) 2)… …   Medical dictionary

  • microsome — n. small granule of protoplasm …   English contemporary dictionary

  • microsome — [ mʌɪkrəsəʊm] noun Biology a fragment of endoplasmic reticulum and attached ribosomes obtained by centrifugation of homogenized cells. Derivatives microsomal adjective …   English new terms dictionary

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