View source for Sucrose gradient centrifugation



==Overview==
'''Sucrose gradient centrifugation''' is a type of [[centrifugation]] often used to purify enveloped [[virus]]es (with densities 1.1-1.2 g/cm³) and [[ribosome]]s, and also to separate cell [[organelle]]s from crude cellular extracts. This method is also used to purify exosomes.<ref>{{cite journal | author=Raposo, G., Nijman, H. W., Stoorvogel, W. et al.| title=B lymphocytes secrete antigen-presenting vesicles.| journal=J. Exp. Med. | year=1996 | volume=183| pages=1161 | url=http://www.jem.org/cgi/content/abstract/183/3/1161?ijkey=92acd76957442efd160b99c26777ac331fc23cc8&keytype2=tf_ipsecsha</ref>

== Equilibrium centrifugation ==

Typically, a sucrose [[Density Gradient|density gradient]] is created by gently overlaying lower concentrations of [[sucrose]] on higher concentrations in a centrifuge tube. For example, a sucrose gradient may consist of layers extending from 70% sucrose to 20% sucrose in 10% increments (though this is highly variable depending on sample to be purified). The sample containing the particles of interest is placed on top of the gradient and centrifuged at forces in excess of 150,000 x g. The particles travel through the gradient until they reach the point in the gradient at which their density matches that of the surrounding sucrose. This fraction can then be removed and subjected to further analysis.

A similar technique is sucrose cushion centrifugation, in which a particle mixture is pelleted through a 20% sucrose layer, coming to rest at the interface with a 70% solution. This allows concentration of particles from a sample. Unlike standard centrifugation, which in effect crushes the particles against the bottom of the centrifuge tube, the sucrose cushion method causes no mechanical stress and allows the collection of morphologically intact particles.

== Non-equilibrium centrifugation ==

This is very similar to the equilibrium form, but the experiment is only run until a particular point. Then the sucrose is eluted from the bottom of the tube.

==References==
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[[Category:Laboratory techniques]]

[[de:Dichtegradientenzentrifugation]]
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