Thiol group determination

Spectroscopic methods of detection and quantitation of thiol groups have dominated the analytical procedures. An ideal reagent for thiol group determination would have the following properties ... 

Al-Ghannam et al. [25] described a simple fluorimetric procedure for determination of three pharmaceutical compounds containing thiol groups, including penicillamine. In this method, the drugs are treated with 1,2-naphthoquinone-4-sulfonic acid. The later compound is reduced to l,2-dihydroxynaphthalene-4-sulfonic acid, which is measured fluorimetrically (excitation = 318 nm, emission = 480 nm). The method is sensitive to 0.5 1.5 pg/mL, with a detection limit of 0.05 pg/mL (S/N = 2). 

Add 1-10 mg of a protein or antibody containing an available thiol group to the particle suspension. Alternatively, add the protein to be coupled to the particle suspension in an amount equal to 1-10 X molar excess over the calculated monolayer for the protein type to be coupled. The optimal amount of protein to be added should be determined experimentally. Creating thiol groups on proteins or peptides may be done from disulfides by reduction. Alternatively, a thiolation reagent may be used to add thiols to the protein surface for coupling (see the protocols in Chapter 1, Section 4.1). 

BM(PEG)2 also can be used to determine protein-protein interactions or subunit interactions if there are available free thiol groups on each protein or subunit. The following protocol can be used to crosslink two thiol-containing proteins. 

Figure 2. Illustration of the importance of the choice of reaction conditions on the determination of initial velocity. Shown are four conditions applied to examine the rate behavior of Escherichia coli NAD+-dependent coenzyme A-linked aldehyde dehydrogenase (Reaction NAD+ + CoA-SH + Acetaldehyde = NADH + Acetyl-S-CoA + H+). All assay mixtures contained enzyme, 0.5 mM NAD+, 8 /jlW CoA-SFI, 16 mM acetaldehyde, and 22.5 mM Tris buffer at pFI 8.1. (a) Time-course observed when enzyme was added to the standard assay (b) time-course observed when enzyme was added to standard assay augmented with 10 mM 2-mercaptoethanol (c) time-course observed when enzyme was first preincubated for 15 min with 8 /jlW CoA-SH, 16 mM acetaldehyde, 10 mM 2-mercaptoethanol, and 22.5 mM Tris buffer at pH 8.1, and the reaction was initiated by addition of NAD+ (d) time-course observed when enzyme was preincubated with lOmM 2-mercaptoethanol for 15 min andthen addedtostandard assay augmented with 10 mM 2-mercaptoethanol. The data are most compatible with the idea that the enzyme has an active-site thiol group that must be reduced to express full catalytic activity during assay.

A FIA method for the determination of captopril was based on the oxidation of the thiol group in the molecule by Ce . This reaction results in the emission of light (chemiluminescence), which can be measured. In this example the dye rhodamine G was used to enhance the emission of light by the reaction. The method developed was rapid and precise. ... 

The power of the exciton chirality method lies in its applicability to molecules having functional groups which are not chromophores in the usual sense (such as hydroxy, amino or thiol groups), but can be converted to a chromophoric derivative, such as an unsaturated or aromatic acyl derivative. This procedure is extremely useful for the determination of the absolute configuration of products of stereoselective synthesis having a hydroxy, amino or thiol group at the stereogenic center. 

Thiol groups have a high affinity for mercury ions including organic mercury derivatives, which are widely used in the determination of protein structures by X-ray crystallography (Section F). Titration of SH groups in proteins is often accomplished with... 

Spin-spin relaxation dynamics were also used in the study of the kinetics of the vulcanization of polysulphide rubbers. The T2 values decrease with the course of the reaction and the time dependence of log (T2/T ), where corresponds to the time equal to zero, exhibits an inflection. The inflection point is attributed to gel formation, and the reaction rate constants for the two separate processes are determined from the T2 data. It was also observed that the addition of carbon black reduces T2 by a factor of 2 or 3, because vulcanization occurs both through the thiol groups and by the chemical reaction between the polymer and carbon black 37>. 

The reaction of OPA with amino acids (see Fig. 10) requires a mercaptan cofactor that is incorporated as part of the final derivative product. The choice of mercaptan can affect derivative stability and chromatographic selectivity (178). Mercaptoethanol is the most commonly used coreagent. Cysteine is not well detected, because this amino acid can react at the a-amine group or it can react via the side chain thiol. Thus, cysteine is determined only after conversion of the thiol group by oxidation or alkylation. Reaction time with OPA is very fast, 1 minute at room temperature. Detection limits are typically in the low picomole range. Representative references include... 

AF Bradbury, DG Smith. The use of 3-bromopropionic acid for the determination of protein thiol groups. J Biochem 131 637-642, 1973. 

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