Sucrose gradient centrifugation
From Free net encyclopedia
Sucrose gradient centrifugation is a type of centrifugation often used for enveloped viruses (with densities 1.1-1.2 g/cm3) and ribosomes purification and also is frequently used for separating cell organelles from crude cellular extracts.
Equlibrium centrifugation
In a typical application of the process, a sucrose density gradient is created by gently overlaying lower concentrations of sucrose on higher concentrations in a centrifuge tube. A sucrose gradient may consist of layers decreasing from 70% sucrose to 20% sucrose in 10% increments (though this is highly variable depending on sample). The sample containing the particles of interest is overlayed on top of the gradient and centrifuged in an ultracentrifuge at forces in excess of 150,000 x g. The particles travel through the gradient and sediment at a point where the sucrose solution matches the particles density. 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.