Bovine Serum Albumin

Bovine serum albumin is a protein whose key biological function is to regulate the colloidal osmotic pressure of blood. BSA is widely used in various studies and applications. Made up of 583 amino acids, BSA is a water-soluble protein with a calculated molecular weight of 66,430 Da. Six α-helices form three homologous domains of BSA. Depending on pH, it undergoes reversible conformational isomerization. The native structure of the protein becomes reactive and flexible on heating.

Bovine Serum Albumin is used for many applications, including the following applications:

• BSA has been used in cell culture, e.g. as a supplement in media prepared for culturing of oligodendrocytes.
• BSA has been used for the dilution of primary antibody solution in immunohistochemistry procedures.
• BSA has been used as a standard in the Bradford method of protein quantification.
• BSA has been used in blocking and permeabilization buffer for immunofluorescence studies.

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

Prepared using heat shock fractionation

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.