plasma membranes were isolated from ah 66 cells , some of which had been labeled with [ 14c ] glucosamine , by the following procedure : homogenization of cells which had been hardened by treatment with zn ions , fractionation of the homogenate by sucrose density gradient centrifugation and purification of the membranes by partition in an aqueous two-phase polymer system .
C0007603
plasma membranes
C0007634
cells