5-Thio-2-nitrobenzoate anion

Probably the most frequently used spectrophotometric method to detect thiol groups, both for non-protein and protein sulphydryl groups involves the use of Ellman s reagent (Scheme 7.5). 5,5 -Dithiobis(2-nitrobenzoic acid), (DTNB) (Ellman 1959) undergoes disulphide exchange with thiol groups and the formation of 5-thio-2-nitrobenzoate anion (TNB) (Scheme 7.6). 

A procedure for identifying certain cholinesterase variants was proposed by Dietz et al. (D15). After a period during which comments and discussion were offered by others working in the field, the method was published in Selected Methods of Clinical Chemistry (D16). This method is based upon the Ellman reaction (ElO), which was used by Ellman et al. (Ell) for the assay of acetylcholinesterase, and by Garry and Routh (G9) for the assay of serum cholinesterase. In these assay procedures, a thiocholine ester is used as the substrate. The thiocholine produced upon hydrolysis reacts with 5,5 -dithiobis(2-nitrobenzoic acid) (DTNB) to yield 5-thio-2-nitrobenzoate anion and other products. The rate of the reaction may be determined by measuring the rate at which... 

Ellman s reagent, 5,5 -dithio-bis-(2-nitrobenzoic acid), or DTNB, is a compound useful for the quantitative determination of sulfhydryls in solution (Ellman, 1958,1959). The disulfide of Ellman s reagent readily undergoes disulfide exchange with a free sulfhydryl to form a mixed disulfide and release of one molecule of the chromogenic substance 5-sulfido-2-nitrobenzoate, also called 5-thio-2-nitrobenzoic acid (TNB). The intense yellow color produced by the TNB anion can be measured by its absor-... 

The colorimetric method is based on the hydrolysis of the substrate acetylthiocholine to acetate and thiocholine as performed by the cholinesterase. Thiocholine is then reacted with 5,5 -dithiobis(2-nitrobenzoic acid) (DTNB) to form a yellow anion (5-thio-2-nitrobenzoate). The latter is quantitated by spectrometric analysis at 405 nm, with the concentration being proportional to the cholinesterase activity in the given sample. Also for a few days postmortem the cholinesterase activity in different tissues is measurable. ... 

The kinetics and mechanism of the reaction of HOSCN/OSCN with 5-thio-2-nitrobenzoic acid (TNB) have been investigated as a function of pH (77). The reaction is first order with respect to [OSCN ] and first order with respect to [TNB]. The observed bell-shaped profile in the 2.5conjugate acid with a conjugate base. Assuming that the acid/base equilibria are rapid, the mechanism of Eqs. (52)-(55) was proposed (where TNB is the carboxylate anion, TNB includes deprotonation of the thiol, and DTNB is the disulfide) ... 

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