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S Vamvakas

Publications and source records attributed to S Vamvakas.

At least 73 records · Page 4Linked to original sources
PubMed1989

Metabolic activation of the nephrotoxic haloalkene 1,1,2-trichloro-3,3,3-trifluoro-1-propene by glutathione conjugation.

1,1,2-Trichloro-3,3,3-trifluoro-1-propene (TCTFP) is structurally closely related to the stable and non-toxic tetrachloroethylene. However, in TCTFP, the trifluoromethyl group enhances chemical reactivity with nucleophiles. This fact suggested that TCTFP may be metabolized intensively by glutathione (GSH) conjugation and therefore, like hexachlorobutadiene, would be expected to be nephrotoxic. We have investigated the nephrotoxicity and metabolism of TCTFP. Administration of 20 and 40 mg/kg to male rats resulted in a large, dose-dependent increase in urinary excretion of gamma-glutamyl transpeptidase (GGT) indicative of proximal tubular damage. No increase in plasma transaminase concentrations indicative of liver damage was found. In rats, N-acetyl-S-(1,2-dichloro-3,3,3-trifluoro-1-propenyl)-L-cysteine was a major urinary metabolite of TCTFP. TCTFP was transformed by microsomal and cytosolic GSH S-transferases from rat liver to S-(1,2-dichloro-3,3,3-trifluoro-1-propenyl)glutathione (DCTFPG) (identified by NMR and mass spectrometry). DCTFPG was toxic to rat renal cortex cells. Inhibition of GGT and cysteine conjugate beta-lyase blocked DCTFPG cytotoxicity. These results suggest the following TCTFP bioactivation: conjugation with GSH in the liver, catabolism of the GSH S-conjugate to the cysteine S-conjugate and cleavage of the cysteine S-conjugate by beta-lyase with formation of reactive intermediates in the kidney.

Animals↗
PubMed1989

Mutagenicity of benzyl S-haloalkyl and S-haloalkenyl sulfides in the Ames-test.

The mutagenicity of benzyl 1,2,3,4,4-pentachlorobutadienyl sulfide (BPBS) and benzyl 1,2-dichlorovinyl sulfide (BDVS) was studied in the Ames preincubation assay to investigate the hypothesis that the mutagenic effect of the cysteine S-conjugates S-(pentachlorobutadienyl)-L-cysteine and S-(1,2-dichlorovinyl)-L-cysteine is associated with their metabolism to unstable thiols. Under conditions enabling cytochrome P-450-dependent benzylic hydroxylation of BPBS and BDVS, both benzyl sulfides were mutagenic. These results in combination with the lack of mutagenicity observed with benzaldehyde and with the tert-butyl analogues, which cannot be metabolized to a hemimercaptal, indicate that the formation of unstable thiols is responsible for the mutagenic effects of the benzyl sulfides and the corresponding cysteine S-conjugates. Benzyl 2-chloro-1,1,2-trifluoroethyl sulfide, which also undergoes benzylic hydroxylation, was negative in the Ames-Test; this is in agreement with the observed lack of mutagenicity of the corresponding S-conjugate S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine. Also, benzyl 2-chloroethyl sulfide, which, along with the corresponding S-conjugate S-(2-chloroethyl)-L-cysteine, does not require bioactivation, was a potent, direct-acting mutagen in the Ames-Test.

Animals↗
PubMed1989

Mutagenicity of tetrachloroethene in the Ames test--metabolic activation by conjugation with glutathione.

The mutagenicity of tetrachloroethene (tetra) and its S conjugate, S-(1,2,2-trichlorovinyl)glutathione (TCVG) was investigated using a modified Ames preincubation assay. TCVG was a potent mutagen in presence of rat kidney particulate fractions containing high concentrations of gamma-glutamyl transpeptidase (GGT) and dipeptidases. Purified tetra was not mutagenic without exogenous metabolic activation or under conditions favoring oxidative metabolism. Preincubation of tetra with purified rat liver glutathione (GSH) S-transferases in presence of GSH and rat kidney fractions resulted in a time-dependent formation of TCVG as determined by (HPLC) analysis and in an unequivocal mutagenic response in the Ames test. Experiments with tetra in the isolated perfused rat liver demonstrated TCVG formation and its excretion with the bile; bile collected after the addition of tetra to the isolated perfused liver was unequivocally mutagenic in bacteria in the presence of kidney particulate fractions. The mutagenicity was reduced in all cases by the GGT inhibitor serine borate or the beta-lyase inhibitor aminooxyacetic acid. These results support the suggestion that cleavage of the GSH S conjugate formed from tetra by the enzymes of the mercapturic acid pathway and by beta-lyase may be involved in the nephrocarcinogenic effects of this haloalkene in rats.

Animals↗
PubMed1989

Cytotoxicity of cysteine S-conjugates: structure-activity relationships.

The cytotoxicity of cysteine S-conjugates was investigated in freshly isolated rat renal proximal tubule cells. The study was designed to determine the contribution of the thiols and of the acylating intermediates formed by cysteine conjugate beta-lyase to the initiation of cytotoxicity. Cell viability was determined by trypan blue exclusion and by lactate dehydrogenase leakage. The S-conjugates S-(1,2,2-trichlorovinyl)-L-cysteine, S-(1,2,3,3,3-pentachloro-prop-1-enyl)-L-cysteine and S-(1,2,3,4,4-pentachlorobuta-1,3-dienyl)-L-cysteine, at a concentration of 0.2 mM, reduced cell viability compared to controls from 85% to less than 50% after 3 h. The alpha-chlorinated enethiols formed from these S-conjugates are transformed to acylating intermediates. The S-conjugate S-(2-chlorovinyl)-L-cysteine forms an enethiol, which cannot transform to an acylating intermediate and did not reduce cell viability at 0.2 mM; at 1 mM, it resulted in a very slight reduction of cell viability after 3 h. S-(pentachlorophenyl)-L-cysteine and S-benzyl-L-cysteine, which form stable thiols after metabolism by beta-lyase, were not cytotoxic at a concentration of 1 mM. The direct acting S-(2-chloroethyl)-L-cysteine (0.2 mM) reduced cell viability after 3 h from 85% to 90% (control) to 40%. The results obtained suggest that reactions of the initial thiol-metabolites with biological macromolecules do not contribute to the induction of cytotoxicity by cysteine S-conjugates and indicate that acylating intermediates formed by cysteine conjugate R-lyase induce cytotoxic effects by non-selective acylation of cellular macromolecules.

Animals↗
PubMed1989

Assessment of unscheduled DNA synthesis in a cultured line of renal epithelial cells exposed to cysteine S-conjugates of haloalkenes and haloalkanes.

The ability of S-(1,2-dichlorovinyl)-L-cysteine (DCVC), S-(1,2,2-trichlorovinyl)-L-cysteine (TCVC), S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine (PCBC), S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine (CTFEC) and S-(2-chloroethyl)-L-cysteine (CEC) to induce DNA repair was investigated in LLC-PK1, a cultured line of porcine kidney tubular epithelial cells. DNA repair due to exposure of the cells to the S-conjugates was determined as unscheduled DNA synthesis (UDS) after inhibition of replicative DNA synthesis in confluent LLC-PK1 monolayers. DCVC, TCVC and PCBC induced dose-dependent UDS in LLC-PK1 at concentrations which did not impair the viability of the cells compared to untreated controls; higher concentrations were cytotoxic, resulting in lactate dehydrogenase leakage into the medium. Cell death was also induced by CTFEC, which failed to exert genotoxicity. CEC induced the highest response among these cysteine conjugates without impairing cell viability. Inhibition of cysteine conjugate beta-lyase with aminooxyacetic acid abolished the effects of DCVC, TCVC, PCBC and CTFEC but did not influence the genotoxicity of CEC.

Animals↗
PubMed1988

Induction of unscheduled DNA synthesis and micronucleus formation in Syrian hamster embryo fibroblasts treated with cysteine S-conjugates of chlorinated hydrocarbons.

S-(chloroethyl)-cysteine (CEC) and S-(1,2-dichlorovinyl)-cysteine (DCVC) have been proposed as intermediates in the metabolic transformation of the carcinogens 1,2-dichloroethane and 1,1,2-trichloroethylene. We have tested the ability of CEC and DCVC to induce DNA repair and genotoxic effects at the chromosomal level by comparative assessment of unscheduled DNA synthesis induction and micronucleus formation in Syrian hamster embryo fibroblasts. CEC induced a potent and dose-dependent response in both assays, whereas DCVC treatment resulted in a comparatively weak induction of DNA repair and failed to raise micronucleus formation above control rates. Inhibition of cysteine conjugate beta-lyase diminished the effect of DCVC, but had no influence on the genotoxicity of CEC either in the unscheduled DNA synthesis or micronucleus assay.

Animals↗
PubMed1988

Bacterial cysteine conjugate beta-lyase and the metabolism of cysteine S-conjugates: structural requirements for the cleavage of S-conjugates and the formation of reactive intermediates.

The cysteine conjugate beta-lyase mediated metabolism and the mutagenicity of the synthetic cysteine conjugates S-(2-chloroethyl)-L-cysteine (CEC), S-(2-chlorovinyl)-L-cysteine (CVC), S-(1,2,3,3,3-pentachloroprop-1-enyl)-L-cysteine (PCPC), S-(pentachlorophenyl)-L-cysteine (PCPhC), S-(chloro-1,2,2-trifluoroethyl)-L-cysteine (CTFEC), S-benzyl-L-cysteine (SBC) and S-methyl-L-cysteine (SMC) were investigated in Salmonella typhimurium strains TA100, TA2638, TA102 and TA98 to establish structure/activity relationships. Bacterial 100,000 X g supernatants cleaved CTFEC, PCPC, CVC, PCPhC and SBC to pyruvate; pyruvate formation was inhibited by the beta-lyase inhibitor aminooxyacetic acid (AOAA) in all cases. Of the compounds tested, CEC, PCPC and CVC were mutagenic in the Ames-test. CTFEC, PCPhC and SBC failed to increase the number of revertants above control levels. The mutagenicity of PCPC and CVC could be inhibited by AOAA. CEC exerted a potent mutagenic effect in the Ames-test which was not affected by AOAA; CEC was not transformed to pyruvate by bacterial beta-lyase. Neither pyruvate formation nor mutagenicity were observed with SMC. These results indicate that the structure of the substituent on the sulfur atom is an important determinant for the biological activity of cysteine S-conjugates. Electronegative and/or unsaturated substituents are required for beta-lyase catalysed beta-elimination reactions. The formation of chemically unstable thiols, which may be converted to thioacylating intermediates, seems to be a prerequisite for beta-lyase dependent mutagenicity of S-conjugates.

Aminooxyacetic Acid↗
PubMed1988

Thioacylating agents as ultimate intermediates in the beta-lyase catalysed metabolism of S-(pentachloro-butadienyl)-L-cysteine.

The transformation of the hexachloro-1,3-butadiene metabolite S-(1,2,3,4,4-pentachlorobuta-1,3-dienyl)-L-cysteine (PCBC) by bacterial cysteine conjugate beta-lyase (beta-lyase) and by N-dodecylpyridoxal bromide (PLP-Br) was investigated using GC/MS to identify products formed. PCBC was transformed by both bacterial beta-lyase and PLP-Br to the major products 2,3,4,4-tetrachlorobutenoic acid and 2,3,4,4-tetrachlorothiobutenoic acid, and to the minor metabolites trichloroacetic acid and S-(1,2,3,4,4-pentachlorobuta-1,3-dienyl)-mercaptoacetic acid. In the presence of diethylamine as model nucleophile, PLP-Br transformed PCBC to yield 2,3,4,4-tetrachlorothiobutenoic acid diethylamide; attempts to trap 1,2,3,4,4-pentachlorobutadienyl thiol, the initial metabolite formed by beta-elimination from PCBC, were unsuccessful. The results obtained suggest that the formation of a thioacylating intermediate (a thioketene or a thiono acyl chloride) may be the decisive reaction during the beta-lyase dependent activation of PCBC.

Butadienes↗
PubMed1988

Mutagenicity of amino acid and glutathione S-conjugates in the Ames test.

The mutagenicity of the glutathione S-conjugate S-(1,2-dichlorovinyl)glutathione (DCVG), the cysteine conjugates S-(1,2-dichlorovinyl)-L-cysteine (DCVC) and S-(1,2-dichlorovinyl)-DL-alpha-methylcysteine (DCVMC), and the homocysteine conjugates S-(1,2-dichlorovinyl)-L-homocysteine (DCVHC) and S-(1,2-dichlorovinyl)-DL-alpha-methylhomocysteine (DCVMHC) was investigated in Salmonella typhimurium strain TA2638 with the preincubation assay. DCVC was a strong, direct-acting mutagen; the cysteine conjugate beta-lyase inhibitor aminooxyacetic acid decreased significantly the number of revertants induced by DCVC; rat renal mitochondria (11,000 X g pellet) and cytosol (105,000 X g supernatant) with high beta-lyase activity increased DCVC mutagenicity at high DCVC concentrations. DCVG was also mutagenic without the addition of mammalian activating enzymes; the presence of low gamma-glutamyltransferase activity in bacteria, the reduction of DCVG mutagenicity by aminooxyacetic acid, and the potentiation of DCVG mutagenicity by rat kidney mitochondria and microsomes (105,000 X g pellet) with high gamma-glutamyltransferase activity indicate that gamma-glutamyltransferase and beta-lyase participate in the metabolism of DCVG to mutagenic intermediates. The homocysteine conjugate DCVHC was only weakly mutagenic in the presence of rat renal cytosol, which exhibits considerable gamma-lyase activity, this mutagenic effect was also inhibited by aminooxyacetic acid. The conjugates DCVMC and DCVMHC, which are not metabolized to reactive intermediates, were not mutagenic at concentrations up to 1 mumole/plate. The results demonstrate that gamma-glutamyltransferase and beta-lyase are the key enzymes in the biotransformation of cysteine and glutathione conjugates to reactive intermediates that interact with DNA and thereby cause mutagenicity.

Acetylcysteine↗
PubMed1988

Mutagenicity of hexachloro-1,3-butadiene and its S-conjugates in the Ames test--role of activation by the mercapturic acid pathway in its nephrocarcinogenicity.

The mutagenicity of hexachloro-1,3-butadiene and its S-conjugates 1-(glutathion-S-yl)-1,2,3,4,4-pentachloro-1,3-butadiene (GTB), 1,4-(bis-glutathion-S-yl-1,2,3,4-tetrachloro-1,3-butadiene (BGTB) and 1,4-(bis-cystein-S-yl)-1,2,3,4-tetrachloro-1,3-butadiene (BCTB) was investigated in Salmonella typhimurium TA100 using a modified preincubation assay. GTB was a direct-acting mutagen; the mutagenic potency of GTB was markedly enhanced by rat kidney microsomes or mitochondria and less so by cytosol. The bis-conjugates BGTB and BCTB were not mutagenic in the strains TA100, TA2638 and TA98. Purified HCBD was not mutagenic either without exogenous metabolic activation or with rat liver microsomes fortified with NADPH. Preincubation with rat liver microsomes and glutathione resulted in an unequivocal mutagenic activity of HCBD which was increased by additional inclusion of rat kidney microsomes. The cysteine conjugate beta-lyase inhibitor aminooxyacetic acid decreased the mutagenicity of HCBD and its S-conjugates. These results provide strong evidence that formation of the corresponding monoglutathione S-conjugate from HCBD and subsequent cleavage of this conjugate by gamma-glutamyltranspeptidase and beta-lyase may be responsible for the nephrocarcinogenicity of the parent compound in vivo, whereas formation of the bis-glutathione S-conjugate probably plays no role in the organ specific effects of HCBD.

Aminooxyacetic Acid↗
PubMed1988

DNA-binding of sulfur-containing metabolites from 35S-(pentachlorobutadienyl)-L-cysteine in bacteria and isolated renal tubular cells.

S-(Pentachlorobutadienyl)-L-cysteine (PCBC) is the penultimate metabolite formed from the nephrocarcinogen hexachlorobutadiene (HCBD). It is activated by cysteine conjugate beta-lyase (beta-lyase) to yield thioacylating metabolites thought to be responsible for PCBC-induced cytotoxicity and mutagenicity. We have investigated the beta-lyase dependent DNA-binding of metabolites formed from 35S-PCBC in Salmonella typhimurium (S. typhimurium) TA100 and in rat renal proximal tubule cells. 35Sulfur was found in DNA isolated from S. typhimurium (410 +/- 93 DNA-adducts per 10(6) nucleotides) and renal cells (68 or 97 DNA-adducts per 10(6) nucleotides). Enzymatic hydrolysis of the isolated DNA to yield 3'-nucleotide phosphates and fractionation of the hydrolysate by HPLC indicated the presence of 3 distinct, 35S-containing metabolites which did not coelute with unchanged 3'-nucleotide phosphates and likely represent DNA constituents modified by 35S-PCBC metabolites. Identical retention volumes were obtained for altered bases isolated from bacteria and from renal cells. The results obtained indicate that PCBC metabolites may covalently bind to DNA and implicate genotoxic mechanisms in HCBD-induced nephrocarcinogenicity.

Animals↗
PubMed1988

Metabolism of hexachloro-1,3-butadiene in mice: in vivo and in vitro evidence for activation by glutathione conjugation.

1. The metabolism of 14C-hexachloro-1,3-butadiene (HCBD) was studied in mice and in subcellular fractions from mouse liver and kidney. 2. In the presence of glutathione (GSH), liver microsomes and cytosol transformed HCBD to S-(pentachlorobutadienyl)glutathione (PCBG). PCBG formation in subcellular fractions from mouse kidney was very limited. Oxidative metabolism of HCBD by cytochrome P-450 could not be demonstrated. 3. Cysteine conjugate beta-lyase was present in mitochondria and cytosol from mouse liver and kidney. 4. After an oral dose of 30 mg/kg 14C-HCBD, mice eliminated 67.5-76.7% of dose in faeces; urinary elimination accounted for 6.6-7.6%. 5. Metabolites of HCBD identified are: S-(pentachlorobutadienyl)glutathione in faeces; S-(pentachlorobutadienyl)-L-cysteine, N-acetyl-S-(pentachlorobutadienyl)-L-cysteine and 1,1,2,3-tetrachlorobutenoic acid in urine. 6. The results suggest that conjugation of HCBD with GSH in liver, followed by renal processing of the glutathione S-conjugates and beta-lyase-catalysed formation of reactive intermediates, accounts for the organ specific toxicity of HCBD in mice.

Animals↗
PubMed1987

Enzymatic transformation of mercapturic acids derived from halogenated alkenes to reactive and mutagenic intermediates.

The metabolism of the mercapturic acids S-pentachlorobutadienyl-N-acetylcysteine (N-Ac-PCBC), S-trichlorovinyl-N-acetylcysteine (N-Ac-TCVC) and S-dichlorovinyl-N-acetylcysteine (N-Ac-DCVC) by subcellular fractions from male rat liver and kidney homogenates was studied. As a model compound, N-Ac-PCBC, 14C labelled, was synthesised. It was intensively metabolised by cytosolic but not by microsomal enzymes from rat liver and kidney. The major metabolite identified by GC/MS was pentachlorobutadienylcysteine, the amount produced being highest in kidney cytosol. Metabolic conversion of 14C-N-Ac-PCBC by kidney and liver cytosol resulted in covalent binding of radioactivity to protein, binding was strongly inhibited by the beta-lyase inhibitor aminooxyacetic acid (AOAA). N-Ac-TCVC and N-Ac-DCVC were also transformed by cytosolic enzymes to the corresponding cysteine conjugates (trichlorovinylcysteine and dichlorovinylcysteine). The three mercapturic acids tested were strong mutagens in the Ames-test after addition of rat kidney cytosol. In the absence of cytosol, N-Ac-TCVC and N-Ac-DCVC were weakly but definitely mutagenic, whereas N-Ac-PCBC was not. In contrast to N-Ac-PCBC, the "direct" mutagens N-Ac-TCVC and N-Ac-DCVC were both transformed to pyruvate by bacterial (S. typhimurium TA100) homogenate 100,000 g supernatants. It is concluded that mercapturic acids are deacetylated to the corresponding cysteine conjugates by cytosolic (N-Ac-PCBC, N-Ac-TCVC and N-Ac-DCVC) and bacterial enzymes (N-Ac-TCVC and N-Ac-DCVC) and further cleaved to reactive and mutagenic intermediates by mammalian and/or bacterial beta-lyase. The observed activation mechanisms for the mercapturic acids, whose formation from hexachlorobutadiene, tetrachloroethylene and trichloroethylene has been proven, might contribute to the nephrotoxicity and nephrocarcinogenicity of the parent alkenes.

Acetylation↗
PubMed1986

Bacterial beta-lyase mediated cleavage and mutagenicity of cysteine conjugates derived from the nephrocarcinogenic alkenes trichloroethylene, tetrachloroethylene and hexachlorobutadiene.

The metabolism of beta-lyase and the mutagenicity of the synthetic cysteine conjugates S-1,2-dichlorovinylcysteine (DCVC), S-1,2,2-trichlorovinylcysteine (TCVC), S-1,2,3,4,4-pentachlorobuta-1,3-dienylcysteine (PCBC) and S-3-chloropropenylcysteine (CPC) were investigated in Salmonella typhimurium strains TA100, TA2638 and TA98. The bacteria contained significantly higher concentrations of beta-lyase than mammalian subcellular fractions. Bacterial 100,000 X g supernatants cleaved benzthiazolylcysteine to equimolar amounts of mercaptobenzthiazole and pyruvate. DCVC, TCVC and PCBC produced a linear time-dependent increase in pyruvate formation when incubated with bacterial 100,000 X g supernatants; pyruvate formation was inhibited by the beta-lyase inhibitor aminooxyacetic acid (AOAA). CPC was not cleaved by bacterial enzymes to pyruvate. DCVC, TCVC and PCBC were mutagenic in three strains of S. typhimurium (TA100, TA2638 and TA98) in the Ames-test without addition of mammalian subcellular fractions; their mutagenicity was decreased by the addition of AOAA to the preincubation mixture. CPC was not mutagenic in any of the strains of bacteria tested. These results indicate that beta-lyase plays a key role in the metabolism and mutagenicity of haloalkenylcysteines when tested in S. typhimurium systems. The demonstrated formation in mammals of the mutagens DCVC, TCVC and PCBC during biotransformation of trichloroethylene (Tri), tetrachloroethylene (Tetra) and hexachlorobutadiene (HCBD) may provide a molecular explanation for the nephrocarcinogenicity of these compounds.

Animals↗
PubMedDate not supplied

The nephrotoxin dichlorovinylcysteine induces expression of the protooncogenes c-fos and c-myc in LLC-PK1 cells--a comparative investigation with growth factors and 12-O-tetradecanoylphorbolacetate.

Previous studies in kidney cells showed that S-(1,2-dichlorovinyl)-L-cysteine (DCVC) induces both direct DNA damage and DNA double-strand breaks by activation of Ca(2+)-dependent endonucleases. The objective of this study was to investigate the effects of DCVC on the expression of the protooncogenes c-fos and c-myc in cultured kidney cells (LLC-PK1). Supplementation of the incubation medium with 10% FCS after 24 hr incubation in 0.2% FCS resulted in a clear, but comparatively weak induction of the expression of c-fos and c-myc in LLC-PK1 cells. Addition of 500 microns DCVC to the high serum incubation medium induced a further three-fold increase of the transcript levels. A similar increase in the absolute amount of c-fos mRNA was induced by a mixture of growth factors (epidermal growth factor/insulin/transferrin) and of c-myc mRNA with 12-O-tetradecanoylphorbolacetate. However, the kinetics of gene expression were different. In the presence of DCVC the expression of c-fos and c-myc increased continuously in a time-dependent manner during the entire incubation period. In contrast, with growth factors and 12-O-tetradecanoyl-phorbolacetate the maximum transcript levels were detected after 0.5 hr (c-fos) and 1 hr (c-myc), respectively; thereafter, a slight decrease was observed up to the end of the incubation time.

Animals↗
PubMedDate not supplied

Thioacylating intermediates as metabolites of S-(1,2-dichlorovinyl)-L-cysteine and S-(1,2,2-trichlorovinyl)-L-cysteine formed by cysteine conjugate beta-lyase.

The bioactivation mechanism of S-(1,2-dichlorovinyl)-L-cysteine (DCVC) and S-(1,2,2-trichlorovinyl)-L-cysteine (TCVC) was studied with cysteine conjugate beta-lyase (beta-lyase) from Salmonella typhimurium and with the pyridoxal phosphate model N-dodecylpyridoxal bromide (PL-Br) as catalysts and with GC/MS to identify the metabolites formed. PL-Br converted S-2-benzothiazolyl-L-cysteine to 2-mercaptobenzothiazole and S-benzyl-L-cysteine to benzyl mercaptan, demonstrating the ability of PL-Br to serve as a model for beta-lyase. PL-Br and bacterial beta-lyase converted DCVC to chloroacetic acid and chlorothionoacetic acid and TCVC to dichloroacetic acid. Incubations of PL-Br with the S-conjugates in the presence of diethylamine resulted in the formation of N,N-diethylchlorothioacetamide from DCVC and of N,N-diethyldichlorothioacetamide from TCVC. Attempts to trap the enethiols, which are the expected initial products formed by beta-elimination, by reaction with methyl iodide in incubations with the beta-lyase model were not successful. The formation of thioacylating agents from the enethiols may contribute to the cytotoxic and mutagenic effects of DCVC and TCVC.

Acylation↗