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Biomedical subjects

W B Jakoby

Publications and source records attributed to W B Jakoby.

At least 37 records · Page 2Linked to original sources
PubMed1986

Role of N-methyltransferases in the neurotoxicity associated with the metabolites of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and other 4-substituted pyridines present in the environment.

Amine N-methyltransferases in the brains of humans, monkeys, mice, rabbits and rats, as well as two homogeneous enzymes isolated from rabbit liver, are capable of N-methylating 4-phenyl-1,2,3,6-tetrahydropyridine to 1-methyl-4-phenyltetrahydropyridine (MPTP), and 4-phenylpyridine to 1-methyl-4-phenylpyridinium ion (MPP+). The product in each instance is a neurotoxin. The suggestion is offered that the known long half-life of methylpyridinium compounds in brain may be due to limitations in transport of such charged metabolites out of this tissue and to metabolic recycling of the desmethyl species by amine N-methyltransferases. The methylation of pyridines to quaternary amines is suggested as a means by which lipophilic compounds, having gained entrance to the cell, are converted to charged species that efflux much less readily.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1986

Amine N-methyltransferases from rabbit liver.

N-Methylation of amines has been ascribed to enzymes listed as amine N-methyltransferase, indolethylamine N-methyltransferase, and arylamine N-methyltransferase. All of these activities are accomplished by each of two related enzymes present in rabbit liver. The two N-methyltransferases have a very broad and overlapping specificity for primary and secondary amines. Both have a molecular mass of 30,000 daltons and react with an antibody formed to one of them, but have different isoelectric points.

Amino Acids↗
PubMed1986

Identification of intratissue sites for xenobiotic activation and detoxication.

Results of immunohistochemical and histochemical investigations on xenobiotic-metabolizing enzymes and aryl hydrocarbon hydroxylase activity have demonstrated that xenobiotic activation and detoxication do not occur uniformly throughout the liver, skin, respiratory tract, and pancreas, four tissues that are targets for the toxic actions of xenobiotics that are biotransformed into reactive metabolites. It has been shown that there can be significant differences in the levels and activities of xenobiotic-metabolizing enzymes among even morphologically similar cells, that an inducer can affect a specific xenobiotic-metabolizing enzyme to significantly different extents within different cells in a tissue, and that inducers of xenobiotic-metabolizing enzymes can alter differentially the extents to which different cells within a tissue participate in xenobiotic metabolism. These studies also have revealed that the route of administration of an inducer can affect significantly the induction of xenobiotic-metabolizing enzymes and aryl hydrocarbon hydroxylase activity within an organ such as the pancreas. Some of the immunohistochemical findings reported for the cellular localizations of xenobiotic-metabolizing enzymes within specific tissues, e.g., the nasal mucosa, may not appear to be entirely consistent with the intratissue distribution of benzo[a]pyrene hydroxylase activity, especially after induction. However, it must be appreciated that other cytochrome P-450 isozymes undoubtedly are present within these tissues which, although not studied, also are capable of catalyzing aryl hydrocarbon hydroxylase activity.

Animals↗
PubMed1986

The ability of amine N-methyltransferases from rabbit liver to N-methylate azaheterocycles.

The substrate specificity of two homogeneous amine N-methyltransferases from rabbit liver has been demonstrated to extend to the azaheterocycles pyridine, R-(+)-nicotine and S-(-)-nicotine. Both enzymes methylate R-(+)-nicotine at the pyridyl nitrogen to afford the N-methylnicotinium salt, whereas S-(-)-nicotine does not act as a substrate for either enzyme. Surprisingly, R-(+)-nicotine is methylated at either the pyridyl nitrogen, or the pyrrolidine nitrogen, to afford the two isomeric monomethylate nicotinium ions when an enzymic preparation containing both methyl transferase activities was used. Under similar conditions S-(-)-nicotine was methylated only at the pyridyl nitrogen. The production of charged metabolites in-vivo, from the large number of pyridino-compounds that are used as drugs, or are present in the environment, may be of toxicological significance, in view of the reported toxicities of several such quaternary ammonium compounds.

Animals↗
PubMed1984

2-Propylthiouracil does not replace glutathione for the glutathione transferases.

2-Propylthiouracil has been reported as replacing glutathione as a substrate for the glutathione transferases of rat liver. This observation has been examined with several homogeneous glutathione transferases that were prepared from human and rat liver by different methods in three laboratories. No evidence was obtained for 2-propylthiouracil as a substrate for glutathione transferase in the several reactions tested.

Animals↗
PubMed1983

Cysteine conjugate beta-lyase.

Cysteine conjugate beta-lyase from rat liver, an enzyme participating in a shunt from mercapturic acid synthesis, has been purified and found to be active with a number of compounds that bear nonpolar leaving groups on the beta-carbon of an amino acid substrate. Pyridoxal phosphate is considered to be a participant in the reaction. In addition to aromatic thioethers of cysteine, the enzyme is also active with two aliphatic amino acid derivatives, S-1,2-dichlorovinyl-L-cysteine and beta-chloroalanine. Evidence is presented that catalysis results in "suicide" inhibition with a partition ratio of about 600 for each of the substrates.

Animals↗
PubMed1982

Immunohistochemical localization of glutathione S-transferases in livers of untreated rats.

Sheep antibodies raised against three isoenzymes of glutathione S-transferase (EC 2.5.1.18), transferases B, C, and E, which were isolated and purified to apparent homogeneity from rat liver, have been employed to localize these enzymes at the light microscopic level within livers of untreated rats. Using these antibodies in an unlabeled antibody peroxidase-antiperoxidase staining technique, each glutathione S-transferase was detected immunohistochemically within parenchymal cells throughout the liver lobule. In addition, immunohistochemical staining for transferases C and E, but not for transferase B, was observed within bile duct epithelium. While all parenchymal cells were stained with each glutathione S-transferase antibody, the patterns of immunohistochemical staining intensity observed across the liver lobule with the three anti-transferases were not uniform: parenchymal cells within the centrilobular region were more intensely stained for each lobular region were more intensely stained for each isoenzyme than were those within the midzonal and periportal regions of the lobule. The results of this immunohistochemical study thus demonstrate that glutathione S-transferases are not distributed uniformly throughout the liver lobule and that each transferase is present in the greatest concentration within the centrilobular region of the lobule.

Animals↗
PubMed1982

Arylamine N-methyltransferase. Methylation of the indole ring.

Arylamine N-methyltransferase catalyzes the novel methylation of the ring nitrogen of tryptamine and pyrrole as well as a number of other arylamines including aniline and its derivatives. S-Adenosyl-L-methionine serves as donor. Tyramine, indole, benzylamine, and desmethylimipramine were inactive as methyl group acceptors. The enzyme was purified from rabbit liver to electrophoretic homogeneity and was characterized as a protein monomer of 27,000 daltons with a pI of 4.8. The kinetic mechanism appears to be rapid equilibrium random Bi-Bi.

Amino Acids↗
PubMed1982

Cysteine S-conjugate N-acetyltransferase from rat kidney microsomes.

An acetyltransferase from rat kidney microsomes that catalyzes the N-acetylation of thioethers of L-cysteine has been solubilized, stabilized, and separated from hydrolytic enzymes active against both the acetylated product, a mercapturic acid, and acetyl coenzyme A. Efficiency of catalysis varies with the lipophilicity of the substituent at sulfur in the order, ethyl less than propyl less than benzyl less than butyl, as predicted by the Hansch pi constants. Although L-tryptophan is acetylated at a very low rate, acetylation is not detectable for L-cysteine, L-methionine, L-serine, L-leucine, L-phenylalanine, or L-glutamic acid. The properties and substrate specificity reported here, along with previous studies on enzyme distribution, suggest that cysteine S-conjugate N-acetyltransferase is responsible for the final step in mercapturic acid biosynthesis.

Acetyltransferases↗
PubMed1981

On the mechanism of aryl sulfotransferase.

Aryl sulfotransferase IV (EC 2.8.2.1), purified to homogeneity from male rat liver, catalyzes the sulfation of a variety of substituted phenols, including catecholamines, tyrosine esters, and peptides containing NH2-terminal tyrosine residues. An investigation of the mechanism of the enzyme was carried out using 2-chloro-4-nitrophenol as a model substrate. Kinetic, inhibition, and binding studies with aryl sulfotransferase IV are all consistent with a random rapid equilibrium Bi Bi kinetic mechanism with two dead end product inhibitor complexes. Studies of the chemical mechanisms of the enzyme-catalyzed reaction demonstrate that electron-withdrawing substituents decrease the maximal velocity of phenol sulfation. The maximal velocity of the reaction correlates with Hammett sigma p- constants (rho = -0.25). Evidence is presented for the mechanism by which adenosine 3',5'-bisphosphate and aryl sulfotransferase catalyze the transfer of sulfate from 2-chloro-4-nitrophenyl sulfate to other phenols.

Animals↗