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Mercapturic Acid

Gas chromatographic analysis of chlorophenylmercapturic acid lindane metabolites.

History of Xenobiotic Metabolism

Mercapturic Acid Formation

The discovery of mercapturic acids occurred in two labs in 1879. E.Baumann and C.Preuss were members of the Physiological Institute of the University of Berlin and examined the metabolism of bromobenzene fed to dogs. They discovered that, in addition to sulfate(s) there was a second sulfur containing metabolite in the urine of the dogs which they named as a mercapturic acid.1

In addition, they found out that hydrolysis of this metabolite yielded acetic acid and para-bromo phenylmercaptan. In the same year M.Jaffe, in Konigsberg, elucidated the biotransformation of chlorobenzene and iodobenzene finding that they also formed mercapturic acids.2 Only 5 years later Baumann reported the correct structure of the mercapturic acids as acetyl cysteine conjugates3

The complete metabolic sequence however, starting with glutathione conjugation, remained unknown for over 70 years. The relationship between glutathione conjugation and the formation of mercapturic acids was initially characterized in 1959 at University of Birmingham by S.P.James, M.M.Barnes P.B.Wood, H.G.Bray and T.J.Franklin. They showed that administration of a mercapturic acid precursor led to a drop in liver glutathione levels commensurate with the amount of mercapturic acid formed.4 They went on to show that S-(p-Cl-benzyl) glutathione was converted in vitro to S-p-Cl benzyl cysteine5 and this compound could be acetylated by liver preparations.6 Two years later, J.Booth, E.Boyland and P. Sims described the direct enzymatic formation of glutathione conjugates7 providing the backdrop for the investigation of glutathione tranferases in modern times.

Gas chromatographic analysis of chlorophenylmercapturic acid lindane metabolites.

Allsup T, Walsh D

An analytical method for phenols has been adapted for the analysis of chlorophenylmercapturic acids in rat urine. Chlorothiophenols were produced from the mercapturic acids by hydrolytic cleavage with sodium hydroxide. Acetate esters of the chlorothiophenols were formed by addition of acetic anhydride to the aqueous alkaline solution. After acylation, the acetate derivatives were extracted into hexane. Forming the acetate esters of the chlorothiophenols prevented their oxidation to disulfides and significantly improved their chromatographic properties. Electron-capture gas chromatographic analysis of the stable acetate esters was performed on a mixed phase column, 4% SE-30 + 6% OV-210. Recoveries of four chlorothiophenols ranged from 82 to 93%. This method required no sample transfer steps; therefore, sample loss and analysis time were minimized.

PMID: 6174537, UI: 82142858



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