Bovine Serum Albumin

Bovine serum albumin (BSA) is a 66.4 kDa, water-soluble protein composed of 583 amino acids. It has a single polypeptide chain with three homologous domains formed by six α-helices. Depending on pH, it undergoes reversible conformational isomerization. The native structure of the protein becomes reactive and flexible on heating. BSA has been used as a model protein in various applications, including immunodiagnostic procedures, cell culture media and clinical chemistry. Serum albumins facilitates drug disposition and efficacy by maintaining osmotic blood pressure.

Bovine Serum Albumin has been used:

• to prevent nonspecific adsorption of fibrin matrices to tissue culture plates
• as a constituent in the preparation of albumin droplets
• as a supplement in L-15 medium to increase spermatogonia number without enhancing the growth of somatic cells
• as a standard protein to evaluate metal oxide adsorption isotherms

Among its many applications, BSA is a fatty acid (FA) carrier. Thus when BSA is used in applications like cell culture, it is important to exercise control over particular FA′s for cell culture, because specific fatty acids can affect different cell lines in a variable manner. In order to control fatty acid content in cell culture, fatty acid-free BSA is useful, for researchers to be able fatty acids specific to their cell lines. Fatty acid-free BSA also allows for optimal and maximum binding sites for the specific FA′s to use in cell culture. The use of FA-free BSA also addresses concerns about endogenous fatty acids that might be potentially present in non-FA-free BSA.

Certain conformational and primary-sequence epitopes of BSA are suspected allergens in human beef and milk allergies.

Prepared using heat shock fractionation. Further purified to reduce fatty acid content.

Serum albumin may be referred to as Fraction V. This naming convention is taken from the original Cohn method of fractionating serum proteins using cold ethanol precipitation. Serum albumin was found in the fifth ethanol fraction using Cohn′s method. Since then, the term "Fraction V" has been used by some to describe serum albumin regardless of the method of preparation. Others have used this term to describe serum albumin purified by ethanol fractionation methods that have been highly modified since the original Cohn method was described. Sigma-Aldrich manufactures and distributes serum albumins purified from a variety of primary methods including the true Cohn fractionation method, modified ethanol fractionation methods, heat shock and chromatography. Additional purification steps may include crystallization or charcoal filtration.