Murine leukemic lymphoblasts: homogenization and fractionation procedures for plasma membrane vesicles isolation

Plasma membrane vesicles were isolated from murine leukemic lymphoblasts L5178Y. The isolation procedure selected involved a method of mechanical disruption in a hypoosmotic-buffered solution and the separation of plasma membrane vesicles by an adaptation of the fractionation method described by D. W. McKeel and L. Jarett for fat cells (J. Cell Biol., 44, 417, 1970). In order to select the homogenization method we took into account several parameters: the extent of cell and nuclear disruption, the integrity of the nuclear membrane, the 5′-nucleotidase activity recovered at the first step of fractionation and the mitochondrial rupture. The homogenization method finally used yielded 89% of cellular rupture with only 9% of nuclear damage. The isolation procedure showed an overall yield of 70–90%. A plasma membrane fraction was isolated with an enrichment in 5′-nucleotidase and ouabain-sensitive (Na⁺K⁺)-ATPase specific activities of 15- and 13-fold, respectively, and essentially free of mitochondrial, lysosomal, and endoplasmic reticulum contamination. The electron microscopy demonstrated that the plasma membrane fraction essentially consisted of smooth vesicles of several sizes.