The bicinchoninic acid assay (BCA Assay) is a biochemical assay for determining the total level of protein in a solution, similar to Bradford protein assay. The total protein concentration is exhibited by a color change of the sample solution from green to purple in proportion to protein concentration, which can then be measured using colorimetric techniques.
Coomassie Blue R (CBR) is sensitive for protein detection in PAGE gels, and protein can be directly quantitated by colorimetric. Coomassie Blue dye binds to peptides in an acidic medium. The color change of this assay is measured at 595 or 600 nm. We calculate the protein concentration using the formula created by standards. This AbVideo displays the procedure of protein quantification by using CBR.
Steps of quantifying protein using UV absorbance (280nm) are demonstrated. 280nm absorbance depends on the Tyr and Trp (amino acids with aromatic rings) content. A very rough protein concentration can be obtained by making the assumption that the protein sample has an extinction coefficient of 1 (1 OD = 1 mg/ml protein).
Silver staining is used to detect proteins after electrophoretic separation on polyacrylamide gels. It combines excellent sensitivity while using very simple and cheap equipment and chemicals. The procedures of silver staining are protein fixation, silver impregnation and image development.