Enzyme-catalysed conjugations of glutathione with unsaturated compounds

Sulphur-containing metabolites of beta-bromostyrene formed by the marmoset, rabbit and rat

1. The administration of beta-bromostyrene to the rat results in a fall in the level of hepatic glutathione. 2. Marmosets, rabbits and rats dosed with beta-bromostyrene excrete two mercapturic acids. One of these, N-acetyl-S-(2-hydroxy-2-phenyl-1-bromoethyl)-cysteine is readily converted into N-acetyl-S-(1-phenyl-2-bromo-2-ethenyl)-cysteine, the structure of which was established by mass spectrometry. 3. Mass spectrometric evidence suggests that the second mercapturic acid is N-acetyl-S-(1-hydroxy-2-phenylethyl)cysteine. 4. Mandelic acid was detected as a metabolite in all three species.

Synergistic effects of phorone on the hepatotoxicity of bromobenzene and paracetamol in mice

Administration of phorone (diisopropylidene acetone), an industrial solvent, to mice caused a rapid depletion of hepatic glutathione, which is due to enzymatic conjugation of phorone with glutathione, mediated by cytoplasmic enzymes of the liver. Whereas phorone, even in high doses, did not show hepatotoxic effects by itself, combined administration of phorone with a subtoxic dose of either paracetamol or bromobenzene strongly enhanced hepatotoxicity of the latter compounds as was judged from a rise in serum transaminase activities. These findings are compatible with the concept of a dose threshold for biologically reactive intermediate compounds which are bioinactivated through glutathione conjugation.

Short-term toxicity of allyl alcohol in rats

Groups of 15 male and 15 female rats were give 0 (control), 50, 100, 200 or 800 ppm allyl alcohol in the drinking water for 15 weeks. There were no effects attributable to allyl alcohol in the results of the haematological examinations or analyses of serum. There was a dose-related reduction in the fluid intake at all treatment levels in both sexes, while growth and food consumption were reduced in both sexes given 800 ppm and in males give 200 ppm. Males given 100 ppm or above and females given 200 or 800 ppm produced less urine than the controls in a period without water or following a water load. The only changes in organ weight that could be attributed to treatment were increased values for the relative weights of liver, spleen and kidney. All 3 organs were affected in both sexes given 800 ppm and the kidneys were also affected in both sexes given 200 ppm and in females given 100 ppm. No effects attributable to allyl alcohol treatment were seen at autopsy or in the histopathological examination. The no-untoward-effect level established in this study was 50 ppm of the drinking water, a level equivalent to an intake in rats of between 4.8 and 6.2 mg allyl alcohol/kg/day.

Excretion of methyl mercury in rat bile: the effect of diethylmaleate, cyclohexene oxide and acrylamide

Diethylmaleate, cyclohexene oxide and acrylamide administered intraperitoneally to rats, have been shown markedly to inhibit biliary excretion of methyl mercury. Simultaneously the sulphhydryl and sulphide content of the bile decreases. These results probably reflect the conjugation of acrylamide, diethylmaleate and cyclohexene oxide to glutathione in the liver, thereby blocking the biliary excretion of methyl mercury. A high concentration of liver glutathione seems to be a prerequisite for the normal translocation of methyl mercury from liver to bile. These results indicate that methyl mercury is transported from liver to bile as a glutathione complex.

Evaluation of nuclear-substituted styryl ketones and related compounds for antitumor and cytotoxic properties

A number of nuclear-substituted styryl ketones, the related Mannich bases, and allyl alcohols were synthesized and evaluated for antitumor activity, principally in the L-1210 lymphoid leukemia and P-388 lymphocytic leukemia screening tests. The cytotoxicity of some of these compounds assessed in Eagle's 9KB carcinoma cell culture system was also recorded. Two of the Mannich bases showed promising levels of activity in the P-388 screening; of the results obtained to date, over one-third of the derivatives showed cytotoxicity at dose levels of 1-3 ppm. Other pharmacological results of these compounds are briefly reported.

Cross specificity in some vertebrate and insect glutathione-transferases with methyl parathion (dimethyl p-nitrophenyl phosphorothionate), 1-chloro-2,4-dinitro-benzene and s-crotonyl-N-acetylcysteamine as substrates

1. Enzymes catalysing the reaction between GSH and methylparathion (dimethyl p-nitrophenyl phosphorothionate), 1-chloro-2,4-dinitrobenzene and S-crotonyl-N-acetylcysteamine were separated by (NH(4))(2)SO(4) precipitation from homogenates of sheep, rat and mouse livers and from homogenates of cockroaches, houseflies and grass grubs. 2. Electrofocusing of the preparations from each of these species separated a number of zones, each of which catalysed the reaction of GSH with all three substrates. 3. Ion-exchange chromatography on CM-cellulose also separated a number of fractions in which activity towards the three substrates coincided. 4. In both separation methods patterns of the activities were consistent with the presence in all species of several GSH transferases each having a degree of cross specificity towards the three substrates.

Biosynthesis of mercapturic acids from allyl alcohol, allyl esters and acrolein

1. 3-Hydroxypropylmercapturic acid, i.e. N-acetyl-S-(3-hydroxypropyl)-l-cysteine, was isolated, as its dicyclohexylammonium salt, from the urine of rats after the subcutaneous injection of each of the following compounds: allyl alcohol, allyl formate, allyl propionate, allyl nitrate, acrolein and S-(3-hydroxypropyl)-l-cysteine. 2. Allylmercapturic acid, i.e. N-acetyl-S-allyl-l-cysteine, was isolated from the urine of rats after the subcutaneous injection of each of the following compounds: triallyl phosphate, sodium allyl sulphate and allyl nitrate. The sulphoxide of allylmercapturic acid was detected in the urine excreted by these rats. 3. 3-Hydroxypropylmercapturic acid was identified by g.l.c. as a metabolite of allyl acetate, allyl stearate, allyl benzoate, diallyl phthalate, allyl nitrite, triallyl phosphate and sodium allyl sulphate. 4. S-(3-Hydroxypropyl)-l-cysteine was detected in the bile of a rat dosed with allyl acetate.

Distribution of enzymes that catalyse reactions of glutathione with alpha beta-unsaturated compounds

1. A study of the distribution of glutathione S-alkenetransferases in the livers of vertebrate species suggests that different enzymes may catalyse reactions of GSH with (i) trans-benzylideneacetone, (ii) 2,3-dimethyl-4(2-methylenebutyryl)phenoxyacetic acid, (iii) cinnamonitrile, (iv) o-chlorobenzylidenemalononitrile, (v) methyl vinyl sulphone, and (vi) 3-(beta-nitrovinyl)indole. 2. Glutathione S-alkenetransferase activity was generally greatest in rat liver, but the enzyme in hamster liver was more active towards o-chlorobenzylidenemalononitrile, and the enzyme in rabbit, hamster, guinea-pig and mouse livers was more active towards methyl vinyl sulphone. 3. Results from studies of the distribution of activities in rat liver and rat kidney, heat inactivation of rat liver supernatants, and (NH(4))(2)SO(4) fractionation and acid-precipitation experiments, differentiated further between some of the enzymes concerned with substrates (i)-(vi). 4. The infrequent detection of mercapturic acids in vivo is discussed.

The conjugation of glutathione with unsaturated acyl thiol esters and the metabolic formation of S-carboxyalkylcysteines

The partial purification and properties of an enzyme from the soluble fraction of rat liver that catalyses the reaction of glutathione with 2,3-unsaturated acyl thiol esters is described, and its possible role in the formation of S-carboxyalkylcysteines is discussed. The synthesis of S-(3-methylcrotonyl)- and S-(2-methylcrotonyl)-N-acetylcysteamine and of S-crotonyl-NN-dimethylcysteamine hydrochloride and dicyclohexylammonium S-crotonyl-N-acetyl-l-cysteine is described.

The reaction of aralkyl sulphate esters with glutathione catalysed by rat liver preparations

1. Rat liver supernatant preparations catalyse the reactions of some aralkyl sulphate esters with GSH to yield S-aralkylglutathione derivatives. 2. A glutathione S-transferase that catalyses these reactions has been purified 16-fold. 3. The purified enzyme preparation catalyses the release of sulphate ions from benzyl sulphate, 1-menaphthyl (naphth-1-ylmethyl) sulphate and phenanthr-9-ylmethyl sulphate only in the presence of GSH. It does not cause the release of sulphate ions from prop-1-yl sulphate, l-serine O-sulphate, phenyl sulphate or oestrone 3-sulphate even when GSH is added. 4. The stability and specificity of the enzyme and its response to inhibitors and to changes of pH were studied. 5. The activity of the preparation was compared with the activities of glutathione S-transferases described previously.

Enzyme-catalysed reactions between some 2-substituted 5-nitrofuran derivatives and glutathione

1. A glutathione transferase present in rat and human liver supernatant catalyses the reaction of some 2-substituted 5-nitrofuran derivatives with GSH, with formation of a conjugate and release of the nitro group as inorganic nitrite. Some of the substrates undergo the same reaction at a slower rate in the absence of enzyme. Nitrofuran derivatives commonly used as drugs, and five other drugs containing nitro groups, did not react. 2. Substrate activity in the nitrofuran derivatives showed an approximate correlation with the lability of the nitro group to alkali. 3. Optimum pH values ranging from 6.6 to 9.0 were found for the enzymic reaction with various derivatives, the values being influenced by alkali-lability and pK values of the compounds. 4. Tenfold purification of rat liver glutathione S-aryl-transferase resulted in an equal purification of the activities that catalyse the reaction of two of the nitrofuran derivatives with GSH.

Glutathione S-aralkyltransferase

1. The name ;glutathione S-aralkyltransferase' is proposed for the enzyme catalysing the reaction of benzyl chloride with GSH. 2. Results from heat-inactivation studies, ammonium sulphate-fractionation and acid-precipitation experiments, and studies of the distribution of activities in rat liver, in rat kidney and in the livers of other animals indicate that glutathione S-aralkyltransferase differs from glutathione S-alkyltransferase, S-aryltransferase, S-epoxidetransferase and an S-alkenetransferase. 3. The distribution of these enzymes in the livers of the animal species examined was different. 4. Glutathione S-alkyltransferase, S-aralkyltransferase and the S-alkenetransferase that are present in rat liver supernatant were inhibited by GSSG, and the nature of the inhibition varied in each case. 5. 3,5-Di-tert.-butyl-4-hydroxybenzyl acetate reacts spontaneously with GSH, but the rat liver-supernatant-catalysed reaction of GSH with this and other aralkyl esters was weak. 6. A probable function of the glutathione S-transferases is the protection of cellular constituents from strong electrophilic agents.

Mercapturic acid formation during the metabolism of arecoline and arecaidine in the rat

1. In the rat, arecoline is converted into arecaidine and both compounds are converted into N-acetyl-S-(3-carboxy-1-methylpiperid-4-yl) -l-cysteine. 2. The structure of the metabolite was established by (a) synthesis, (b) conversion into N-acetyl-S-(3-methoxycarbonyl-1-methylpiperid-4-yl) -l-cysteine methyl ester, which was chromatographically identical with the synthetic material, and (c) n.m.r.-and i.r.-spectral analysis of the 3-methoxycarbonyl derivative. 3. In ethanolic solution, or in phosphate buffer at pH7.0, arecoline reacted with N-acetyl-l-cysteine to give N-acetyl-S-(3-methoxycarbonyl-1-methylpiperid-4-yl) -l-cysteine; under similar conditions, arecaidine reacted more slowly to give N-acetyl-S-(3-carboxy-1-methylpiperid-4-yl) -l-cysteine. 4. The reaction between arecoline and glutathione or N-acetyl-l-cysteine occurred maximally at neutral pH and decreased rapidly with increasing acidity. At neutral pH, the reactions were bimolecular and second-order when the reactants were in approximately equimolar concentrations and pseudo-unimolecular first-order when arecoline was in large excess. 5. Consideration of the pK(a) values and degrees of ionization of the reactants and the effect of pH on the stoicheiometry of reaction between arecoline and glutathione or N-acetyl-l-cysteine indicated that reaction between un-ionized species occurred more readily than nucleophilic addition (Ad(N)) reactions involving charged intermediates.

Enzymes catalysing conjugations of glutathione with alpha-beta-unsaturated carbonyl compounds

1. Heat-inactivation experiments, ammonium sulphate-fractionation studies, enzyme-inhibition studies with S-(alphabeta-diethoxycarbonylethyl)glutathione, and evidence from the distribution of activities in rat liver, in rat kidney and in the livers of other animals, indicate that reactions of glutathione with (i) trans-benzylideneacetone, (ii) cyclohex-2-en-1-one, (iii) trans-cinnamaldehyde, (iv) diethyl maleate, (v) diethyl fumarate and (vi) 2,3-dimethyl-4-(2-methylenebutyryl)phenoxyacetic acid are catalysed by different enzymes. 2. Evidence is presented that the enzymes catalysing the reactions of glutathione with substrates (i)-(iv) are different from glutathione S-alkyltransferase, S-aryltransferase and S-epoxidetransferase. 3. The name ;glutathione S-alkenetransferases' is proposed for enzymes catalysing reactions of glutathione with alphabeta-unsaturated compounds. 4. The Arrenhius plot for the enzyme-catalysed reaction of diethyl maleate with glutathione is discontinuous, with lower energy of activation at 38 degrees .