Plasma membrane is one of the most studied cellular membranes. Prokaryotic and eukaryotic organisms possess plasma membranes which, in summary, enclose and protect the cytosol, and cellular organelles while communicating to their surroundings due to their semi-permeable characteristics. Plasma membranes are selectively permeable lipid bilayers: they allow nutrients and other metabolites to be transported into the cytosol and allow for export of cellular waste at the same time. Oxygen, CO2 and other gaseous or lipophilic small molecules freely diffuse across the plasma membrane; however, ions, amino acids and sugars follow strict passive and active cellular transportation mechanisms. The plasma membrane lipid bilayer is primarily composed of four phospholipids: phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and sphingomyelin. Phosphatidylinositol, a fifth phospholipid, is also localized in the inner side of the membrane. Additionally, many proteins are embedded or found adhered to both sides of the plasma membrane. For example, glycoproteins are usually found attached to the outer side of the membrane. Assay Genie’s Plasma Membrane Isolation Kit provides a proprietary set of reagents and buffers designed to enable optimized extraction and isolation of intact plasma membrane from mammalian tissues and cells. The protocol requires an ultracentrifuge to be performed and can be completed in a few hours.

Figure: (A) Representation of an ultracentrifuge tube with density gradient from steps 9 through 11. Each fraction (labeled a-h)
corresponds to ~2 ml volume. Following ultracentrifugation, the isolated plasma membrane fraction (labeled as fraction g) is localized at the interface between the 2.5% and 25% density layers (denoted by the bold shaded line). (B) Cholesterol content by fraction, assayed using Assay Genie’s Total Cholesterol Cholesteryl Ester Assay Kit. Cholesterol is highly enriched in the plasma membrane (approximately 22% of the total lipid content of the plasma membrane), but is found in much lower concentration (2%-6% of total lipids) in other organelle membranes.