Bovine serum albumin

Bovine serum albumin (also known as BSA or 'Fraction V') is a serum albumin protein derived from cows. It is often used as a protein concentration standard in lab experiments. Bovine serum albumin (also known as BSA or 'Fraction V') is a serum albumin protein derived from cows. It is often used as a protein concentration standard in lab experiments. The nickname 'Fraction V' refers to albumin being the fifth fraction of the original Edwin Cohn purification methodology that made use of differential solubility characteristics of plasma proteins. By manipulating solvent concentrations, pH, salt levels, and temperature, Cohn was able to pull out successive 'fractions' of blood plasma. The process was first commercialized with human albumin for medical use and later adopted for production of BSA. The full-length BSA precursor protein is 607 amino acids (AAs) in length. An N-terminal 18-residue signal peptide is cut off from the precursor protein upon secretion, hence the initial protein product contains 589 amino acid residues. An additional six amino acids are cleaved to yield the mature BSA protein that contains 583 amino acids.