ABSTRACT
It is estimated that about 30% of the many kinds of proteins in the cell are embedded in cellular membranes1 and that more that 50% of current drug targets are membrane proteins.2,3 Consequently, isolation of membranes and analysis of membrane proteins is of interest across a variety of disciplines. Isolation of the total cellular membrane fraction is straightforward; however, it is more diffi cult to separate membranes from individual organelles. The isolation of the plasma membrane is a particular challenge, due to its low abundance in relation to mitochondria, endoplasmic reticulum, and other membranes in the cell, its similarity to these other membrane components, and its propensity to exist in a variety of structures during isolation, including both open sheets and vesicles.4,5 The procedure reported here is a modifi cation of Jacobson’s cationic colloidal silica technique,6,7 which leads to 20-fold enrichment of the plasma membrane. Proteins are solubilized from the isolated plasma membrane into Laemmli buffer suitable for sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS PAGE) and proteomic analysis. At least 50% of the proteins identifi ed are traditionally assigned to the plasma membrane, and some theoretical membrane proteins are characterized.
