Bovine serum albumin (BSA) is commonly used in cell culture protocols, particularly where protein supplementation is necessary and the other components of serum are unwanted. In cell culture, its main role is as a carrier of small molecules. Because of its negative charge, Bovine Serum Albumin binds water, salts, fatty acids, vitamins and hormones, then carries these bound components between tissues and cells. The binding capacity also makes Bovine Serum Albumin an effective scavenger to remove toxic substances, including pyrogens, from the medium.
Albumins are readily soluble in water and can only be precipitated by high concentrations of neutral salts such as ammonium sulfate. The solution stability of Bovine Serum Albumin is very good (especially if the solutions are stored as frozen aliquots). Albumins are frequently used as stabilizers for other solubilized proteins (e.g., labile enzymes). However, albumin is readily coagulated by heat. When heated to 50°C or above, albumin quite rapidly forms hydrophobic aggregates which do not revert to monomers upon cooling. At somewhat lower temperatures aggregation is also expected to occur, but at relatively slower rates.
Albumin is used to solubilize lipids, and is also used as a blocking agent in Western Blot or ELISA applications.