Ellman’s reagent assay

5,5-Dithio-bis-(2-nitrobenzoic acid) (DTNB) is commonly used for the detection and quantification of free sulfhydryl groups, and can be used to detect the free thiol generated from CoA after an acetyltransferase adds the acetyl-group from acetyl-CoA to an amino group of a protein [97, 98]. The reaction of DTNB with the free thiols can be followed spectrophotometrically at 412 nm [99]. This in vitro assay is suitable for both epsilon and alpha-acetylation, since free CoA is the product for both reactions, and allows for the determination of kinetic parameters of enzymes. This method, however, is better suited for purified proteins and is sensitive to reducing agents that may be present in protein preparations.