摘要:

AbstractThe enzyme mercaptopyruvate sulfurtransferase appears to play an important role in the in vivo detoxification of cyanide. It does so by transferring sulfur to cyanide to produce thiocyanate, which is less toxic and may be excreted through the kidney. Several compounds were tested for their ability to affect the rate of enzyme catalyzed thiocyanate formation in vitro. The studies were carried out using both a partially purified bovine kidney extract and a highly purified enzyme preparation. Hypotaurine and methanesulfinic acid doubled sulfurtransferase activity in the partially purified extract at 30 mM, but inhibited the purified enzyme to 57% (hypotaurine) and 27% (methanesulfinic acid) of control activity at the same concentration. Pyruvate, phenylpyruvate, oxobutyrate, and oxoglutarate each inhibited the extract and purified forms of mercaptopyruvate sulfurtransferase. Phenylpyruvate was the most effective inhibitor, reducing activity to 0.2% of control values in the extract, and 11% of control values for purified MPST when added to the reaction at 30 mM. Other compounds tested (see Table 1) had a negligible effect on sulfurtransferase activity. A heat stable cofactor was found in boiled kidney extract which stimulated sulfurtransferase activity in the extract but inhibited sulfurtransferase activity in the purified enzyme, as was observed for hypotaurine and methanesulfinate. The boiled extract had no thiocyanate forming activity of its own. The cofactor operated in synergy with methanesulfinate, but independently of hypotaurine.

ISSN:0887-2082    

DOI:10.1002/jbt.2570070203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractLantadene C (22β‐2‐methylbutanoyloxy ‐3‐oxoolean‐12‐en‐28‐oic acid) isolated from the leaves of the hepatotoxic plantLantana camara var. aculeata(Red) has been found to be identical with dihydrolan‐tadene A reported earlier. Molecular structure of lantadeneChas been deduced from single crystal X‐ray diffraction analysis. It resembles lantadene A in the pentacyclic portion of the molecule but differs in the side chain region. Atom C‐34is cisto C‐35 in lantadeneCbut istransin lantadene A. Semisynthetic lantadeneCwas prepared by catalytic hydrogenation of lantadene A. LantadeneCwas obtained in two forms, I and II. Form I was crystalline while form II was amorphous. Unlike lantadene A, both form I and II of lantadeneCelicited strong hepatotoxic response in guinea pigs associated with decrease in fecal output, feed intake, hepatomegaly, hepatic injury at the cellular and subcellular level, increase in plasma bilirubin, and acid phosphatase activity. All the clinical signs, hepatic lesions, and changes in blood plasma typified lantana toxicity. This is the first report on the hepatotoxicity of lantadene C. The interrelation of molecular structure and biological activity of lantadene A

ISSN:0887-2082    

DOI:10.1002/jbt.2570070204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractAdministration of 4, 4′dipyridyl to rats induces the activities of xenobiotic transferases (phase II drug metabolizing enzymes), UDP‐glucuronosyl‐tranferase and glutathione‐S‐transferase, and also the concentration and activity of cytochrome P450 (a phase I drug metabolizing enzyme). 2, 2′Dipyridyl, an isomer possessing iron chelation properties, only induces the phase II enzymes. Although the magnitude of the phase II induction by 2, 2′dipyridyl increases with increasing dosages, the selective induction of only phase II activities remains inviolate. Co‐administration of 2, 2′dipyridyl does not prevent 4, 4′dipyridyl from inducing cytochrome P450, suggesting that the iron chelation property is not the factor that precludes 2, 2′dipyridyl from coordinately inducing cytochrome P450

ISSN:0887-2082    

DOI:10.1002/jbt.2570070205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractSeveral diphenyl ether herbicides, such as acifluorfen methyl, have been previously shown to cause large accumulations of the heme and chlorophyll precursor, protoporphyrin, in plants. Lightinduced herbicidal damage is mediated by the photoactive porphyrin. Here we investigate whether diphenyl ether herbicides can affect porphyrin synthesis in rat and chick hepatocytes. In rat hepatocyte cultures, protoporphyrin, as well as coproporphyrin, accumulated after treatment with acifluorfen or acifluorfen methyl. Combination of acifluorfen methyl with an esterase inhibitor to prevent the conversion of acifluorfen methyl to acifluorfen resulted in a greater accumulation of porphyrins than caused by acifluorfen methyl or acifluorfen alone. In vitro enzyme studies of hepatic mitochondria isolated from rat and chick embryos demonstrated that protopor‐phyrinogen oxidase, the penultimate enzyme of heme biosynthesis, was inhibited by low concentrations of acifluorfen, nitrofen, or acifluorfen methyl with the latter being the most potent inhibitor. These findings indicate that diphenyl ether treatment can cause protoporphyrin accumulation in rat hepatocyte cultures and suggest that this accumulation was associated with the inhibition of protoporphyrinogen oxidase. In cultured chick embryo hepatocytes, treatment with acifluorfen methyl plus an esterase inhibitor caused massive accumulation of uroporphyrin rather than protoporphyrin or coproporphyrin. Specific isozymes of cytochrome P450 were also induced in chick embryo hepatocytes. These effects were not observed in the absence of an esterase inhibitor. These results suggest that diphenyl ether herbicides can cause uroporphyrin accumulation similar to that induced by other cytochrome P450‐inducing chemicals such as polyhalogenated aromatic hydrocarbons in the chick hepatocyte sys

ISSN:0887-2082    

DOI:10.1002/jbt.2570070206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe susceptibility of liver microsomes to lipid peroxidation was evaluated in seven species: rat, rabbit, trout, mouse, pig, cow, and horse. Lipid peroxidation was measured as thiobarbituric acid reactive substances formed in the presence of either FeCl3‐ADP/ascorbate or FeCl2/H2O2initiating systems. For rat, rabbit, and trout microsomes, the order of susceptibility to peroxidation was rat>rabbit>>trout. The lack of peroxidation in trout microsomes could be explained by high microsomal vitamin E levels. Membrane fatty acid levels differed between species. Docosahexaenoic acid predominated in the trout, arachidonic acid in the rat, and linoleic acid in the rabbit. The contribution of individual fatty acids to lipid peroxidation reflected the degree of unsaturation with docosahexaenoic>arachidonic>>>linoleic. For all species except trout, the predicted susceptibility to peroxidation, based on the response of individual fatty acids, agreed well with directly measured microsomal peroxidation. With the exception of the trout, vitamin E content ranged from 0.083–0.311 nmol/mg microsomal protein between species, and low levels did not influence susceptibility to peroxidation. Trout microsomes peroxidized only after vitamin E depletion by prolonged incubation. The data indicate that below a vitamin E threshold, species differences in membrane susceptibility to peroxidation can be reasonably predicted based only on content of individual peroxidizable fatty ac

ISSN:0887-2082    

DOI:10.1002/jbt.2570070207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractA series of in vivo and in vitro experiments were conducted to determine the effects of 2, 3, 7, 8‐tetrachlorodibenzo‐p‐dioxin (TCDD) administered on the expression of c‐ras.Differences in c‐rasexpression between control and TCDD treated groups were determined by immunoassay of p21rasprotein, or indirectly measured by the specific binding of3H‐GTP to hepatic plasma membrane preparations. Intraperitoneal injection of sublethal doses of TCDD significantly elevated (P<0.05, Student t test) levels of hepatic p21rasprotein in Sprague‐Dawley rats and TCDD sensitive C57BL/6J mice. Such an increase occurred at an early stage of poisoning in the C57BL/6J mice. The earliest increase was detectable 6 hr after dosing, and the differencebecame statistically significant by 12 and 24 hr after dosing. In contrast, TCDD tolerant DBA/2J mice had only a marginal increase in hepatic p21rasprotein which did not become statistically significant even at 24 hr post‐dosing. TCDD evoked increases in hepatic p21rasprotein of C57BL/6J mice were accompanied by the increase in the specific binding of GTP to hepatic plasma membranes. Column chromatography of solubilized rat hepatic membrane proteins on sephadex G‐50 showed TCDD administration increased levels of a3H‐GTP binding protein with MW of approximately 21 Kd.3H‐GTP binding in total hepatic membranes was also elevated (P<0.05, Fisher PLSD multiple comparison test) 6 hr and 24 hr after dosing of C57BL/6J mice, but as expected the effect of TCDD was not as conspicuous as that found in the plasma membrane. TCDD treatment increased levels of a 21 Kd protein found in the in vitro translation products of RNA purified from guinea pig liver. This protein was identified as a c‐rasprotein based upon its ability to bind GTP, precipitation by a polyclonal antibody against the rasHa and Ki proteins and subsequent SDS‐PAGE which showed a singl

ISSN:0887-2082    

DOI:10.1002/jbt.2570070208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe recently reported that nitrogen dioxide (NO2), an environmental oxidant, alters the dynamics of the plasma membrane lipid bilayer structure, resulting in increased phosphatidylserine content and angiotensin II (Ang II) receptor binding. Angiotensin II is known to elicit receptor‐mediated stimulation of diacylglycerol (DAG) production in pulmonary artery endothelial cells. Because protein kinase C (PKC) is a phosphatidylserine‐dependent enzyme and is activated by DAG, we examined whether NO2resulted in activation and/or translocation of PKC from predominantly cytosolic to membrane fractions of these cells. We also evaluated whether NO2exposure resulted in increased production of DAG in pulmonary artery endothelial cells. Exposure to 5 ppm NO2for 1–24 hr resulted in significant increases in PKC activity in the cytosolic and membrane fractions (p<0.05 for both fractions) compared to activities in control fractions. Exposure to Ang II resulted in translocation of PKC activity from cytosol to membrane fractions of both control and NO2‐exposed cells. This translocation of PKC from cytosolic to membrane fraction was prevented by the specific receptor antagonist [Sar1Ile8] Ang II. Exposure of 5 ppm NO2for 1–24 hr provoked rapid increases in [3H]glycerol labeling of DAG in pulmonary artery endothelial cells. These results demonstrate that exposure to NO2increases the production of second messenger DAG and activates PKC in both the cytosolic and membrane fractions, whereas Ang II stimulates the redistribution of PKC from cytosolic to membrane fractions of pulmonary artery endothel

ISSN:0887-2082    

DOI:10.1002/jbt.2570070209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effects of the organophosphorus anticholinesterase paraoxon on the binding of radioactive ligands to the M3subtype of the muscarinic receptor and receptor‐coupled synthesis of second messengers in intact rat submaxillary gland (SMG) cells were investigated. The binding of [3H]quinuclidinyl benzilate ([3H]QNB) was most sensitive to atropine and the M3‐specific antagonist 4‐DAMP followed by pirenzepine and least sensitive to the cardioselective M2antagonist AFDX116. This, and the binding characteristics of [3H]4‐DAMP, confirmed that the muscarinic receptors in this preparation are of the M3subtype. Activation of these muscarinic receptors by carbamylcholine (CBC) produced both stimulation of phosphoinositide (PI) hydrolysis and inhibition of cAMP synthesis, suggesting that this receptor subtype couples to both effector systems.Paraoxon (100 μM) reduced Bmaxof [3H]4‐DAMP binding from 27 ± 4 to 13 ± 3 fmol/mg protein with nonsignificant change in affinity, suggesting noncompetitive inhibition of binding by paraoxon. Like the agonist CBC, paraoxon inhibited the forskolininduced cAMP formation in SMG cells with an EC50of 200 nM, but paraoxon was>500 fold more potent than CBC. However, while the inhibition by CBC was counteracted by 2 μM atropine, that by paraoxon was unaffected by up to 100 μM atropine. It suggested that this effect of paraoxon was not via binding to the muscarinic receptor. Paraoxon did not affect β‐adrenoreceptor function in the preparation, since it did not affect the 10 μM isoproterenol‐induced cAMP synthesis, which was inhibited totally by 10 μM propranolol and partially by CBC. Paraoxon had a small but significant effect on CBC‐stimulated PI metabolism in the SMG cells. It is suggested that paraoxon binds to two different sites in these SMG cells. One is an allosteric site on the M3muscarinic receptor which affects ligand binding and may modulate receptor function. The other site may be on the Giproteinadenylyl cyclase system, and produces CBC‐like action, that is, inhibition of the forskolin‐stimulated [3H]cAMP synthesis, and is unaffected by atropine inhibition of the muscarinic receptor. This adds to the complexity of paraoxon actions on muscarinic receptors

ISSN:0887-2082    

DOI:10.1002/jbt.2570070210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractRicin toxin, which consists of two distinct polypeptide moieties, A and B chains, is cytotoxic to the cultured macrophage cell line, J774A.1. Ricin is a protein synthesis inhibitor, and incubating macrophages for 4 hours with ricin (1 pM to 10 nM) in standard medium containing calcium and magnesium inhibited3H‐leucine incorporation into protein (97%, at 1 nM ricin). However, in Ca2+‐free medium, protein synthesis was inhibited only 19%. EGTA pretreatment (to deplete intracellular calcium) also partly protected cells from protein synthesis inhibition, in spite of added calcium (2 mM) in the incubation medium. Decreased toxicity in the absence of extracellular calcium resulted from decreased toxin binding. Adding or deleting Mg2+did not affect protein synthesis or binding of125I‐ricin in cultured macrophages. We conclude that calcium is required for ricin to exert its inhibitory effect on protein synthesis in cultured macrop

ISSN:0887-2082    

DOI:10.1002/jbt.2570070211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:0887-2082    

DOI:10.1002/jbt.2570070202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY