Microsome
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In cell biology, a microsome is a small vesicle that is derived from fragmented endoplasmic reticulum produced when cells are homogenized. They contain the cell's cytochrome p450 enzymes, involved in oxidative metabolism.
Liver microsomes are used for determination of EROD activity as an indicator of CYP1A1-dependent enzymatic activity. The term microsome refers to a mixture of fragmented endoplasmic reticulum (ER) vesicles present in a cell homogenate after mechanical breakage (homogenization) of tissues such as liver. These microsomes can be concentrated and separated from the other cellular organelles by means of differential centrifugation. Different cellular organelles possess different and unique sedimentation velocities and sediment out of aqueous solution at different centrifugal forces. Unbroken cells, nuclei and mitochondria sediment out at 10,000g, while soluble enzyme and fragmented ER which contains the P450s stay in the solution. At a higher speed, 100,000g, ER sediments out of solution as pellet and the soluble enzymes stay in the supernatant. In this way, P450s in microsomes are concentrated and isolated. Microsomes appear as reddish brown color due to the presence of heme in P450s. P450s are highly abundant in livers of rats, mice and humans.
See also
- S9 fraction (postmitochondrial fraction).