The phenolic group of tyrosine and tryptophan residues (amino acid) in a protein will produce a blue purple color complex , with maximum absorption in the region of 660 nm wavelength, with Folin- Ciocalteau reagent which consists of sodium tungstate molybdate and phosphate. Thus the intensity of color depends on the amount of these aromatic amino acids present and will thus vary for different proteins. Most proteins estimation techniques use Bovine Serum Albumin (BSA) universally as a standard protein, because of its low cost, high purity and ready availability. The method is sensitive down to about 10 µg/ml and is probably the most widely used protein assay despite its being only a relative method , subject to interference from Tris buffer, EDTA, nonionic and cationic detergents, carbohydrate, lipids and some salts. The incubation time is very critical for a reproducible assay. The reaction is also dependent on pH and a working range of pH 9 to 10.5 is essential.
Egg albumin was first isolated through successive salt precipitations in 1889, and the procedure was later improved in the first part of the 20th century. The standard purification procedures are labor intensive and difficult to mechanize, which meant that large-scale production of pure Egg albumin was not feasible. With the development of a purification procedure using chromatography techniques, production of extremely pure Egg albumin in commercial volumes is possible.
Egg albumin is very similar in amino acid content to bovine serum albumin (BSA) and can be an excellent substitute for BSA. The tyrosine and tryptophan in BSA are 5.1 g/100g and 0.6 g/100g of protein, while in Egg albumin are 3.9 g/100 g and 1.2 g/100 g of protein, respectively, hence the concentration range may be similar to each other.
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