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T M Guenthner

Publications and source records attributed to T M Guenthner.

At least 55 records · Page 3Linked to original sources
PubMed1981

Cytosolic and microsomal epoxide hydrolases are immunologically distinguishable from each other in the rat and mouse.

Antibodies raised to homogeneous rat liver microsomal epoxide hydrolase were used to distinguish microsomal epoxide hydrolase from epoxide hydrolase of cytosolic origin in mice and rats. Using double diffusion analysis in agarose gels, we show that anti-rat liver microsomal epoxide hydrolase forms a single precipitin line with solubilized microsomes from rat and mouse liver, but no reaction is seen with the corresponding cytosolic fractions. Rat or mouse microsomal epoxide hydrolase activity (using benzo[a]pyrene 4,5-oxide as substrate) can be completely precipitated out of solubilized preparations by the antibody, which is equipotent against rat and mouse microsomal epoxide hydrolase. No precipitation of cytosolic hydrolase activity (using trans-beta-ethyl styrene oxide as substrate) is seen with any concentration of the antibody tested. Thus, in the case of microsomal epoxide hydrolase, extensive immunological cross-reactivity exists between the two species, rat and mouse. In contrast, no cross-reactivity is detectable between cytosolic and microsomal epoxide hydrolase, even when enzymes from the same species are compared. We conclude that microsomal and cytosolic epoxide hydrolase activities represent distinct and immunologically non-cross-reactive protein species.

Animals↗
PubMed1981

The effects of modulation of microsomal epoxide hydrolase activity on microsome-catalyzed activation of benzo[alpha]pyrene and its covalent binding to DNA.

The effects of modulation of microsomal epoxide hydrolase activity on the binding of calf thymus DNA of benzo[alpha]pyrene metabolically activated by rat liver microsomes were investigated. In systems where microsomal epoxide hydrolase levels were not manipulated, 2 major bound species, one derived from 9-hydroxybenzo[alpha]pyrene and the other derived from benzo[alpha]pyrene 7,8-dihydrodiol, were found in approximately equivalent amounts. When epoxide hydrolase levels were increased, either by addition in vitro of purified enzyme or by induction in vivo by trans-stilbene oxide, the binding of the benzo[alpha]pyrene 7,8-dihydrodiol product was increased, while the binding of the 9-hydroxybenzo[alpha]pyrene product was practically eliminated. When microsomal epoxide hydrolase activity was decreased by selective inhibition with low concentrations of 1,1,1-trichloropropene 2,3-oxide, the binding of the species derived from 9-hydroxybenzo[alpha]pyrene was increased several-fold, while that of the species derived from benzo[alpha]pyrene 7,8-dihydrodiol was greatly decreased. The results indicate that the binding species derived from 9-hydroxybenzo[alpha]pyrene is formed through a metabolic pathway leading to an epoxide which is a substrate of microsomal epoxide hydrolase and that microsomal epoxide hydrolase is important in regulating the pattern of binding of individual microsomally-formed benzo[alpha]pyrene metabolites to DNA.

Animals↗
PubMed1981

Modulation of the covalent binding of aryl hydrocarbon metabolites to DNA in vitro after treatment of rats and mice with trans-stilbene oxide.

The effect of trans-stilbene oxide (TSO) induction on the microsome-catalyzed binding of polycyclic aromatic hydrocarbon metabolites to DNA was investigated using two rodent species (Sprague-Dawley rat and C57BL/6N or NMRI Swiss mouse) and 2 different binding substrates (benzo[a]anthracene). It was determined that TSO exerts 2 separate effects on polycyclic aromatic hydrocarbons - it increases the rate of oxidation at the K-region of the molecule due to its induction of specific monooxygenases, and it increases the rate of deactivation of epoxide intermediates by induction of microsomal epoxide hydrolase activity. The importance of these individual effects were determined by inducing monooxygenase activity with BP, altering region specificity and inducing epoxide hydrolase (EH) activity with TSO, assessing the combined inductive effects of TSO and BP, inhibiting EH with 1,1,1-trichloropropene oxide, or increasing its activity by the addition of pure enzyme. This study shows that these effects are similar for both substrates examined, and that the effect of TSO on the binding to DNA of highly carcinogenic bay-region diol-epoxides is multi-faceted, due to its multiple inductive effects.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1980

On the effect of cellular nucleophiles on the binding of metabolites of 7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene and 9-hydroxybenzo(a)pyrene to nuclear DNA.

The binding to DNA of products resulting from the further activation of trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene and 9-hydroxybenzo(a)pyrene was studied in several incubation systems. In a system containing purified DNA and rat liver microsomes, products of 9-hydroxybenzo(a)pyrene were the predominant binding species. In a system containing isolated rat hepatocytes, the total binding was much lower, and products of trans-7,8-dihydroxy-7, 8-dihydrobenzo(a)pyrene predominated. Both the total amounts and the ratios of the bound species were altered by the addition of various soluble nucleophiles to the incubation system. The binding of 9-hydroxybenzo(a)pyrene to both nuclear and purified DNA was decreased in the presence of "non-specific" protein in the incubate. A decrease in the binding of trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene to either purified or nuclear DNA was seen after the addition of active cytosol, but not with protein alone. Either denaturation of the cytosol, or depletion of glutathione by diethylmaleate treatment, partially negated this effect. We conclude that the binding of benzo(a)pyrene metabolites to DNA in the cell is decreased by soluble nucleophiles, and that this trapping of metabolites is selective. 9-Hydroxybenzo(a)pyrene metabolites are removed by non-specific protein binding, whereas removal of trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene metabolites requires higher affinity binding or enzymatic conjugation.

Animals↗
PubMed1979

2,3,7,8-Tetrachlorodibenzo-p-dioxin: covalent binding of reactive metabolic intermediates principally to protein in vitro.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is metabolized by the mouse liver cytochrome P-450-mediated monooxygenase system to reactive intermediates which bind 'covalently' to cellular macromolecules. Although very difficult to quantitate, the presumably covalent binding to microsomal protein occurs between 120 and 2,640 times more readily than binding to deproteinized DNA in the in vitro reaction. Because of the extremely high rate of binding to protein rather than to DNA, it is visualized that TCDD metabolites may be so reactive that they bind in or near the P-450-active site where the TCDD is monoxygenated. This extreme reactivity may preclude the formation of detectable quantities of phenols, dihydrodiols, or conjugated products. The rate of TCDD metabolism is estimated to be between 9,000 and 36,000 times lower than the rate of P-450-mediated benzo[a]pyrene metabolism. To our knowledge, this is the first demonstration that TCDD is metabolized in any organism. There remains the possibility, however unlikely, that this covalently-bound radioactivity represents metabolites of contaminants--present in the radiolabeled TCDD sample in very minute amounts--rather than metabolites of tritiated TCDD itself. The possible relationship between P-450-mediated metabolism of this environmental contaminant and its extreme toxicity or teratogenicity is discussed.

Animals↗
PubMed1978

Evidence in rat and mouse liver for temporal control of two forms of cytochrome P-450 inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin.

In the liver of perinatal rats or mice, the ratio of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced aryl hydrocarbon hydroxylase to total cytochrome P-450 content decreases, whereas the ratio of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced acetanilide 4-hydroxylase to total cytochrome P-450 content increases, between 18 or 19 days and 22 days following conception. The ontogenesis of inducible aryl hydrocarbon hydroxylase corresponds well with increases in a 56000-Mr electrophoretic band; we suggest this band represents the cytochrome P1-450 subunit. The later temporal expression of inducible acetanilide 4-hydroxylase closely parallels 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced increases in size of a 54000-Mr electrophoretic band and a 2--3-nm hypsochromic shift in the Soret peak of the total microsomal reduced cytochrome P-450 . CO complex. We suggest this band represents the cytochrome P-448 subunit. Previous work from this laboratory has shown that this developmental difference is separated by several weeks in rabbit liver, as compared with several day's separation shown in this report with rat or mouse liver. The data here therefore provide evidence in the rodent for temporal control of the expression of different structural gene products regulated by the Ah locus.

Aging↗