Certain features of will be down for maintenance the evening of Friday August 18th starting at 8:00 pm CDT until Saturday August 19th at 12:01 pm CDT.   Please note that you still have telephone and email access to our local offices. We apologize for any inconvenience.

Albumin from Bovine Serum

Product No. B2518

CAS Number: 9048-46-8
Synonyms: Bovine Serum Albumin; Bovine Plasma Albumin; BSA


The molecular weight of BSA has frequently been cited as 66,1201 or 66,2672, but it was revised in 1990 to 66,4303. All three values are based on amino acid sequence information available at the time of publication. BSA is a single polypeptide chain consisting of about 583 amino acid residues and no carbohydrates. At pH 5-7 it contains 17 intrachain disulfide bridges and 1 sulfhydryl group.1,3

Physical Properties

pI in Water at 25°C: Fatty Acid Depleted8 - 5.3, Endogenous Material5,6,7 - 4.7; 4.9  
pH of 1% Solution:1,4 5.2-7  
Optical Rotation:1,9 [α]259: -61°; [α]264: -63°  
Stokes Radius (rs):10 3.48 nm  
Sedimentation constant,1 S20,W X 1013 4.5 (monomer), 6.7 (dimer)
Diffusion constant,1 D20,W X 107 5.9
Partial specific volume,1 V20 0.733
Intrinsic viscosity,1 η 0.0413
Frictional ratio,1 f/f0
Overall dimensions,1 Å 40 X 140
Refractive index increment1 (578 nm) X 10-3 1.90
Optical absorbance,1 0.667
Mean residue rotation,1 [m']233 8443
Mean residue ellipticity1
21.1 [θ]209 nm; 20.1 [θ]222 nm
Estimated α-helix,1 %
Estimated β-form,1 %

Solubility / Solution Stability

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 BSA is very good (especially if the solutions are stored as frozen aliquots). In fact, albumins are frequently used as stabilizers for other solubilized proteins (e.g., labile enzymes). However, albumin is readily coagulated by heat.11 When heated to 50°C or above, albumin quite rapidly forms hydrophobic aggregates which do not revert to monomers upon cooling.4 At somewhat lower temperatures aggregation is also expected to occur, but at relatively slower rates.

Method of Preparation

  1. HISTORY:1,4 Albumin is relatively simple to isolate and purify. One of the first methods of isolation involved extensive dialysis of serum against water; this process removed most globulins. A second procedure took advantage of the good solubility of albumin at low to moderate ammonium sulfate concentrations, and effected precipitation by lowering the pH. Electrophoretic isolation was also employed, as was affinity chromatography. None of these methods were applicable to large scale production.

  2. INITIAL ISOLATION: Initial isolation is by Heat Treatment or by Alcohol Precipitation. Most commercial preparations are now prepared by Alcohol Precipitation a method developed by E. J. Cohn and his associates in the 1940's ("Fraction V" yields albumin with a purity of about 96%) or by Heat Treatment.12

  3. FURTHER PURIFICATION:1,4 Additional removal of impurities can be accomplished by crystallization, preparative electrophoresis, ion exchange chromatography, affinity chromatography (e.g., ConA-agarose removes glycoproteins), heat treatment (removes globulins), low pH treatment, charcoal treatment, organic solvent precipitation (i.e., isooctane), and low temperature treatment.13 Charcoal treatment and organic solvent precipitation remove fatty acids.13

Product Description / Usage14

Albumins are a group of acidic proteins which occur plentifully in the body fluids and tissues of mammals and in some plant seeds. Unlike globulins, albumins have comparatively low molecular weights, are soluble in water, are easily crystallized, and contain an excess of acidic amino acids. Serum and plasma albumin is carbohydrate-free and comprises 55-62% of the protein present.

Albumin binds water, Ca2+, Na+, and K+. Due to a hydrophobic cleft, albumin binds fatty acids, bilirubin, hormones, and drugs. The main biological function of albumin is to regulate the colloidal osmotic pressure of blood. Human and bovine albumins contain 16% nitrogen and are often used as standards in protein calibration studies. Albumin is used to solubilize lipids, and is also used as a blocking agent in Western blots or ELISA applications. Globulin free albumins are suitable for use in applications where no other proteins should be present (e.g., electrophoresis).

Choosing a Product

Please refer to the table below for a complete description of each product. Based on customer input, literature reports, and Sigma's own use, the following table lists product numbers which have successfully been used for specific applications. The list is not comprehensive, and product numbers not listed may often be substituted.

Application Product Number(s)
Antibody purification
Binding and transport studies A4378, A7030, A0281, A3675, A3902, A6003
Blood banking reagents A2153, A4503, A7888, A3294, A3912, A7906, A7030
Culture media (microbial) A2153, A4503, A3294, A3912, A7906, A9430, A7638, A6003
Cell culture (general) A8806, A9418
Electrophoresis (M.W. standard) A7517
ELISA (blocking reagent) A2153, A4503, A4378, A7030, A9430, A3902
ELISA (non-specific binding) A3294
Enzyme systems A2153, A4503, A7888, A3294, A3912, A4378, A7906, A7030, A9430, A7638, A3675
Hapten carrier A7030, A6003, A0281
Immunocytochemistry A9647, A7906, A6793
Immunohematology A2153, A4503, A7888, A3294, A3912, A4378, A7906, A7030, A0281, A6003
Mitogenic assays A2058
Molecular biology B251815, B889415, B6917, B8667, B4287
Protein base or filler A2153, A4503, A3912, A4378, A7906, A7030
Protein supplement (controls) A2153, A4503, A4378, A7906, A7030, A3675
Protein standard (M.W., amino acids, nitrogen) A2153, A4503, A4378, A7030
RIA systems A7888, A4378, A7030, A3675, A3902
Serology A4503, A3912, A4378, A7906, A7030, A9430, A3675



  1. The Plasma Proteins: Structure, Function and Genetic Control, 2nd ed., Frank W. Putnam, ed., Vol. 1, p. 141, 147, Academic Press, New York (1975).
  2. Reed, R.G. et al., Biochem. J., 191, 867 (1980).
  3. Hirayama, K., BBRC, 173(2), 639 (1990).
  4. Sigma data.
  5. Dawson, R.M.C. et al., Data for Biochemical Research, 3rd ed., p. 381, Clarendon Press, Oxford (1993).
  6. Malamud, D. and Drysdale, J.W., Anal. Biochem., 86, 620 (1978).
  7. Righetti, P.G. and Caravaggio, T., J. Chromatog., 127, 1 (1976).
  8. Kaplan, L.J. and J. F. Fostes. et al., Biochem., 10(4), 630-636 (1971).
  9. CRC Handbook of Biochemistry: Selected Data for Molecular Biology, H.A. Sober, ed., p. C-56, The Chemical Rubber Company, Cleveland (1968).
  10. Axelsson, I., J. Chromatog., 152, 21 (1978).
  11. Lewis, Sr., R.J. Hawley's Condensed Chemical Dictionary, 12th ed., p. 30, Van Nostrand Reinhold Co., New York (1993).
  12. Cohn, E.J. et al., J. Am. Chem. Soc., 68, 459 (1946).
  13. Saifer, A. and Goldman, L. J. Lipid Res., 2(3), 268 (1961).
  14. Scott, T. and Eagleson, M., Concise Encyclopedia: Biochemistry, 2nd ed., pp. 19-20, Walter de Gruyter, New York (1988).
  15. These products are acetylated to inactivate nucleases commonly found in BSA, and are thus not listed in the table of unmodified BSA's on pp. 4-9 of this data sheet. Since tyrosines in the BSA are also derivatized, these preparations are not recommended for use as protein standards.


05/02/00 - MAC