- Initial intraorgan formation of mercapturic acid
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The disposition of S-benzyl-glutathione (BSG) in male Wistar rats was evaluated by the HPLC method to examine whether the kidney and liver contributed independently to the biosynthesis of S-benzyl-N-acetylcysteine (BNAc), a mercapturic acid (Chart 1). After intravenous injection, BSG was rapidly transported in both the kidney and the liver at a ratio of about 7:3. Simultaneously, a large amount of BNAc was found in both the kidney and the liver. In the kidney, S-benzyl-cysteine (BCys) reached a maximum concentration (Cmax) at 2 min after BSG injection, whereas BNAc reached Cmax within 3 to 5 min. The generation of BNAc was also observed in the liver. While renal BNAc reached Cmax within 3 to 5 min, hepatic BNAc reached Cmax around 5 min after BSG injection. Moreover, the elimination half-life of the BNAc after intravenous injection of the BSG was equivalent to that observed after intravenous injection of the BNAc itself. These results demonstrate that the kidney contributes to the initial intraorgan generation of BNAc and that this mercapturic acid is also synthesized in the liver and preferentially excreted into urine.
- Sano,Ikegami,Uesugi
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Read Online
- Molecular identification of NAT8 as the enzyme that acetylates cysteine S-conjugates to mercapturic acids
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Our goal was to identify the reaction catalyzed by NAT8 (N-acetyltransferase 8), a putative N-acetyltransferase homologous to the enzyme (NAT8L) that produces N-acetylaspartate in brain. The almost exclusive expression of NAT8 in kidney and liver and its predicted association with the endoplasmic reticulum suggested that it was cysteinyl-S-conjugate N-acetyltransferase, the microsomal enzyme that catalyzes the last step of mercapturic acid formation. In agreement, HEK293T extracts of cells overexpressing NAT8 catalyzed the N-acetylation of S-benzyl-L-cysteine and leukotriene E4, two cysteine conjugates, but were inactive on other physiological amines or amino acids. Confocal microscopy indicated that NAT8 was associated with the endoplasmic reticulum. Neither of the two frequent single nucleotide polymorphisms found in NAT8, E104K nor F143S, changed the enzymatic activity or the expression of the protein by≥2-fold, whereas a mutation (R149K) replacing an extremely conserved arginine suppressed the activity. Sequencing of genomic DNA and EST clones corresponding to the NAT8B gene, which resulted from duplication of the NAT8 gene in the primate lineage, disclosed the systematic presence of a premature stop codon at codon 16. Furthermore, truncated NAT8B and NAT8 proteins starting from the following methionine (Met-25) showed no cysteinyl-S-conjugate N-acetyltransferase activity when transfected in HEK293T cells. Taken together, these findings indicate that NAT8 is involved in mercapturic acid formation and confirm that NAT8B is an inactive gene in humans. NAT8 homologues are found in all vertebrate genomes, where they are often encoded by multiple, tandemly repeated genes as many other genes encoding xenobiotic metabolism enzymes.
- Veiga-da-Cunha, Maria,Tyteca, Donatienne,Stroobant, Vincent,Courtoy, Pierre J.,Opperdoes, Fred R.,Van Schaftingen, Emile
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experimental part
p. 18888 - 18898
(2011/04/17)
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- Cobalt assisted cleavage of S-S bonds and a base-free synthesis of mercapturic acids
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Base free transformation of PhSSPh to sulfides, PhSR (R = alkyl, benzyl, allyl, acyl) and N-acetyl-L-cystine to mercapturic acids [AcNHCH(COOH)CH2SR, R = alkyl, benzyl, allyl, acyl] have been achieved using Zn/cat. CoCl2/organic halide in MeCN at room temperature.
- Chowdhury, Shantanu,Roy, Sujit
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p. 2149 - 2152
(2007/10/03)
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