centrigugation gradient - (Mar/11/2006 )

what is centrifugation gradient??
can someone answer me the method of percoll gradient and metrizimide gradient.
what is the fuction of this gradient.

Do a simple google search for "centrifugation gradient" and you will find some interesting links... (or just combine the definitions of a gradient and of centrifugation, knowing that centrifugation is based on getting the more dense things down in your tubes...).