摘要:

Abstract3‐Mercaptopyruvate sulfurtransferase (E.C. 2.8.1.2; MST) is an enzyme believed to function in the endogenous cyanide (CN) detoxification system because it is capable of transferring sulfur from 3‐mercaptopyruvate (3‐MP) to CN, forming the less toxic thiocyanate (SCN). To date, 3‐MP is the only known sulfur‐donor substrate for MST. In an effort to increase the understanding of what chemical properties of 3‐MP affect its utilization as a substrate, in vitro enzyme kinetic studies of MST were conducted using two mercaptic acids that are structurally related to 3‐MP. Neither of these compounds was able to serve as a sulfur‐donor substrate for MST. Inhibitor studies determined that 3‐mercaptopropionic acid did not affect theKmof MST for 3‐MP but did decreaseVmaxand, thus, was determined to be a noncompetitive inhibitor. Alternatively, 2‐mercaptopropionic acid 2‐MPA decreasedKmandVmaxand was determined to be an uncompetitive inhibitor of MST with respect to 3‐MP. These data indicate that the α‐keto group of 3‐MP is necessary for its utilization as a substrate, and the inhibitor studies suggest that the position of the sulfur may also affect the binding of these compounds to the enzyme. These observations increase the understanding of what factors can affect the utilization of a compound as a sulfur‐donor substrate for MST and may aid in the development of alternative sulfur‐donor substrates fo

ISSN:0887-2082    

DOI:10.1002/jbt.2570100602

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe expression of hepatic glucose‐6‐phosphate dehydrogenase (G6PDH, E.C. 1.1.1.49) is hypothesized to be modulated by free radicals during oxidative stress. The ability of diquat, a compound known to enhance oxidative stress through generation of reactive oxygen species, to modulate the expression of G6PDH in primary cultures of Fischer‐rat hepatocytes was examined. Diquat‐treated hepatocytes maintained in a chemically defined medium showed both a time‐ and concentration‐dependent increase in G6PDH enzyme activity. This increase in enzyme activity was accounted for by an increase in both G6PDH mRNA and immunoreactive protein, suggesting control at a pretranslational level. The possibility that diquat increased transcription by transfecting cells with a chimeric gene containing 935 bp of the G6PDH promoter (‐878 to +57) linked to the gene for chloramphenicol acetyl‐transferase (CAT) was examined. Hepatocytes transiently transfected with this chimera, and subsequently treated with diquat, exhibited an increase in CAT activity. However, hepatocytes transfected with a chimera containing 287 bp of the G6PDH promoter (‐230 to +57) exhibited only basal CAT activity in the presence of diquat. These results suggest that regions in the DNA sequences required for diquat‐induced expression of G6PDH lie between base pairs ‐878 and ‐230 of the G6PDH gene. These findings are suggestive that oxidative stress in hepatocytes increased the expression of G6PDH activity and protein and that the increased expression is controlled at the transcriptional level. © 1

ISSN:0887-2082    

DOI:10.1002/jbt.2570100603

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

年代:1995

数据来源: WILEY

摘要:

AbstractInduction of P450 3A1 and P450 3A2 was studied in adult rat liver following treatment with a single high dose of dexamethasone (DEX). The increase of both P450 3A1 and 3A2 occurred at the level of mRNA as well as protein. P450 3A isozymes thus induced were catalytically active. No constitutive expression of P450 3A1 mRNA or protein was observed in males or females. Constitutive expression of P450 3A2 mRNA and protein was observed in males but not in females. Additionally, in females, P450 3A2 was almost nondetectable compared to that in males, at any dose of DEX. A time course study following DEX treatment showed that P450 3A1 mRNA and protein were detectable in both sexes at 12 hours, increased until 48 hours, and then declined. The decline was more rapid in males. P450 3A2 mRNA and protein increased as early as 3 hours, increased further up to 48 hours, and slowly declined thereafter. A dose‐response study indicated that P450 3A1 mRNA and protein progressively increased in both sexes from a dose of 30 mg/kg. In contrast, P450 3A2 mRNA and protein in males did not increase up to a dose of 30 mg/kg but increased at higher doses. Total P450 content and P450 3A catalytic activity were also found to increase with time and dose. © 1996 John Wiley&Sons, I

ISSN:0887-2082    

DOI:10.1002/jbt.2570100604

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

年代:1995

数据来源: WILEY

摘要:

AbstractNitrogen dioxide (NO2) is a well‐known environmental air toxin, produced from a variety of sources, including cigarette smoke. Because of the growing knowledge of the harmful effects of passive smoking on children, we decided to study the effect of NO2exposure on the release of surfactant from isolated neonatal type II pulmonary epithelial cells. After isolation from 1 to 4 day old rabbits, type II epithelial cells were allowed to adhere for 18 hours, washed, media changed, and were exposed to either 5% CO2in room air or NO2, 5 ppm, for 2 hours (all results mean ± sd; comparisons, pairedt‐test). There was no difference in cell number or viability prior to exposure. Cells exposed to NO2had an increase in LDH release [LDH activity in media/(LDH in media + cells) x 100], air 12.6 ± 2.2%, NO221.7 ± 3.7%, (p<0.05). NO2‐exposed cells also had an increase in total phospholipid (μg/cell culture dish) in media compared to air exposed, air 170.13 ± 7.54, NO2195.15 ± 11.2, (p<0.05).3H‐choline incorporation as a precursor to disaturated phosphati‐dylcholine (DSPC) was also conducted during exposure to either air or NO2. Incorporation of3H‐choline into surfactant lipid was increased in media from cells after NO2exposure compared to air, 58.23 ± 15.16 air, 76.81 ± 19.86 NO2(cpm/μg protein;p<0.05). These results show that 2 hours of 5 ppm NO2exposure is associated with an increase in release of surfactant from neonatal type II cells in culture. © 1996

ISSN:0887-2082    

DOI:10.1002/jbt.2570100605

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe involvement of oxidative stress in the toxicity of chromium (VI) and chromium (III) has been proposed. We have therefore examined the effects of these cations on the production of superoxide anion, nitric oxide (NO), and DNA single strand breaks (SSB) in J774A.1 macrophage cells in culture as well as the effects on lactate dehydrogenase (LDH) leakage and cell viability. Following a 48 hour incubation, over twofold increases in superoxide anion and NO production were observed at concentrations of approximately 0.30 and 50 μM for Cr (VI) and Cr (III), respectively. The patterns of cell viability and LDH leakage paralleled superoxide anion and NO production for Cr (VI) and Cr (III). A 50% decrease in viability was observed at approximately the concentrations that produced a twofold increase in superoxide and NO production. Concentration‐dependent increases in DNA‐SSB were observed after incubation with Cr (III) with maximum increases occurring at a concentration of approximately 60 μM. Cr (VI) had no effect on the incidence of DNA‐SSB at any of the tested concentrations. The results indicate that Cr (VI) and Cr (III) are toxic to the J774A.1 cell line, and the toxicity may be due at least in part to an oxidative stress induced by the production of reactive oxygen species. © 1996 John Wiley&S

ISSN:0887-2082    

DOI:10.1002/jbt.2570100606

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

年代:1995

数据来源: WILEY

摘要:

AbstractRicin, a toxic lectin from the castor bean, affects the cardiovascular system. Because calcium is very important in cardiotoxicity and cell intoxication, we studied the effects of ricin pretreatment to rabbits on basal intracellular calcium levels and calcium uptake and release from isolated papillary muscle, microsomes, and mitochondria. An increase in basal intracellular calcium levels was observed. Ricin pretreatment nearly doubled the intracellular‐free Ca2+concentration as measured by fura‐2 fluorescence microscopy in isolated myocytes (p= 0.002). Ricin did not alter basal calcium efflux in isolated papillary muscles. However, ricin inhibited the NE‐induced calcium efflux (expressed as fractional efflux ratios) in papillary muscles from rabbits receiving the minimum lethal dose of ricin at 25–35 minutes (p= 0.002 and 0.003, respectively). Ricin depressed basal calcium uptake into isolated papillary muscles at 5 minutes (mean ± SEM, μmol/g wet weight) (control: 3.68 ± 0.57; ricin: 2.31 ± 0.28,p= 0.045,n= 6). Ricin pretreatment significantly depressed calcium uptake into microsomes (mean ± SEM, μmol/g protein) (control: 9.9 ± 1.9; ricin: 3.1 ± 1.9,p= 0.025,n= 6). Calcium uptake into mitochondria was increased at the beginning (2 minutes,p= 0.048), but not thereafter. Thus, administration of ricin disturbed calcium homeostasis in the rabbit heart, which may be at least partially responsible for altering cardiac function and myocardial cell death. © 1996 John

ISSN:0887-2082    

DOI:10.1002/jbt.2570100607

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

年代:1995

数据来源: WILEY

摘要:

AbstractA mitochondrial freeze/thaw lysate was fractionated on a DEAE‐cellulose column into four distinct acyl‐CoA ligase fractions. First to elute was a 50 kDa short‐chain ligase that activated only short‐chain fatty acids. Next to elute were three ligases that had activity toward both medium‐chain fatty acids and xenobiotic carboxylic acids; these were termed xenobiotic/medium‐chain ligases (X‐ligases) and labeled XL‐I, XL‐II, and XL‐III, respectively, based on order of elution. The molecular weight of X‐ligases I, II, and III were ca. 55,000, 55,500 and 53,000, respectively. Form XL‐III showed no pH optimum; the rate increased steadily with pH beginning from pH 7.0. XL‐I and XL‐II showed the same behavior with benzoate as substrate, but with medium‐chain fatty acids, both forms had a pH optimum at 8.8. The three X‐ligases differed in substrate specificity. XL‐I was the predominant nicotinic acid activating form and had the lowestKmfor benzoate. Form XL‐II was the only form with measurable salicylate activity, although it was extremely low. XL‐III was the only 2,4,6,8‐decatetraenoic acid activating form and also was the predominant medium‐chain fatty acid‐activating form. By comparison of substrate specificities, it was concluded that the two previously reported ligase preparations were mixtures of the three forms. When the ligase rates were compared to previously determined N‐acyltransferase rates toward benzoyl‐CoA and phenylacetyl‐CoA, the data showed that ligase activities are 100‐fold lower, and thus the ligase is rate limiting for the conjugation of bot

ISSN:0887-2082    

DOI:10.1002/jbt.2570100608

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

年代:1995

数据来源: WILEY

ISSN:0887-2082    

DOI:10.1002/jbt.2570100601

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

年代:1995

数据来源: WILEY