Bovine serum albumin
|according to PDB 3V03|
BSA, Allergen Bos d 6
|Mass / length primary structure||583 amino acids , 66,463 Da|
|Precursor||607 amino acids , 69,293 Da|
Bovine serum albumin (BSA, synonymous with bovine serum albumin ) is a protein from the blood serum of domestic cattle ( Bos taurus ). Because of its low cost, it is used for various purposes in biochemistry when any pure protein is required.
Bovine serum albumin occurs mainly in the blood plasma of cattle , where it is the most abundant protein. It has a high binding capacity for polar substances such as water , Ca 2+ , Na + , K + , as well as for less polar substances such as fatty acids , hormones , bilirubin and various drugs . Its main function is the regulation of colloid osmotic pressure in the blood . It is also the main transport protein for zinc ions and binds about 80% of the Zn 2+ in the blood plasma. BSA has one binding site for Cu 2+ at position 27 and four binding sites for Zn 2+ at positions 91, 123, 270 and 272. After translation it undergoes various post-translational modifications such as proteolysis of the signal peptide (position 1-18), proteolysis behind two basic amino acids at position 24, methylations and phosphorylations . In addition, BSA has disulfide bridges . BSA has been described as the Bos d6 allergen and is found in beef and cow's milk .
The homology of BSA to human serum albumin is only 75.8% at the amino acid level. The isoelectric point at 25 ° C is pH 4.7. The pH value of a one percent solution of BSA is between 5.2 and 7. The isoionic point (pH value of BSA without ions) is pH 5.2. The dimensions are approximately 140 Å × 40 Å × 40 Å, the Stokes radius is 34.8 Å. The extinction coefficient at a wavelength of 279 nm is 43.824 M −1 cm −1 . The rotation value [α] 259 is -61 ° and for [α] 264 -63 °. The sedimentation coefficient of BSA S 20, W is 4.5 × 10 −13 s for the monomer and 6.7 × 10 −13 s for the dimer. The diffusion constant D 20, W is 5.9 × 10 −7 cm 2 / s. The partial specific volume V 20 is 0.000733 m 3 kg −1 . The intrinsic viscosity is η = 4.13 cm³ / g at pH 5.13. The extinction A 279 nm 1 g / L is 0.667. The helical proportion of BSA is 54% and the leaflet proportion 18%. MOPS can increase the thermostability of bovine serum albumin in solutions.
A peptide of the BSA in positions 165 to 173 has been described as a neurotensin-related peptide (NRP) and erroneously described as being involved in the regulation of the digestion of fats , the uptake of lipids and the blood flow.
Commercially purified BSA is also referred to as fraction V , named after the fraction in the Cohn extraction after Edwin J. Cohn . It is used in standard series to determine protein concentration , e.g. B. Bradford test , Lowry test , biuret reaction and BCA test . In the SDS-PAGE , BSA is used as the comigration standard . In the polymerase chain reaction , it is used to bind inhibitors .
When Western blot , the ELISA , the ELISpot , in immunohistochemistry , and generally in immunostaining in immunoassays it is used as part of the blocking solution. As a result, non-specific protein-binding areas are saturated with BSA, which reduces the adsorption of other, more expensive proteins on the surfaces of the reaction vessels used or on blot membranes . BSA is also used in the hybridization of nucleic acids in Denhardt's solution to block unspecific binding sites for proteins and nucleic acids ; it is used accordingly in Southern blot and Northern blot . BSA is also added to some restriction enzymes . However, it is less helpful in avoiding protein adsorption than 0.2 mM octoxinol 9 (synonym Triton X-100 and Nonidet P40), or solutions of 3% (m / V) polyvinylpyrrolidone -40 with a mild detergent such as 0, 05% (m / V) Tween 20 .
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