Effects Of Metabolic Activation Research Articles

Identification of Key Toxic Substances Considering Metabolic Activation: A Combination of Transcriptome and Nontarget Analysis.

There have been numerous studies using effect-directed analysis (EDA) to identify key toxic substances present in source and drinking water, but none of these studies have considered the effects of metabolic activation. This study developed a comprehensive method including a pretreatment process based on an in vitro metabolic activation system, a comprehensive biological effect evaluation based on concentration-dependent transcriptome (CDT), and a chemical feature identification based on nontarget chemical analysis (NTA), to evaluate the changes in the toxic effects and differences in the chemical composition after metabolism. Models for matching metabolites and precursors as well as data-driven identification methods were further constructed to identify toxic metabolites and key toxic precursor substances in drinking water samples from the Yangtze River. After metabolism, the metabolic samples showed a general trend of reduced toxicity in terms of overall biological potency (mean: 3.2-fold). However, metabolic activation led to an increase in some types of toxic effects, including pathways such as excision repair, mismatch repair, protein processing in endoplasmic reticulum, nucleotide excision repair, and DNA replication. Meanwhile, metabolic samples showed a decrease (17.8%) in the number of peaks and average peak area after metabolism, while overall polarity, hydrophilicity, and average molecular weight increased slightly (10.3%). Based on the models for matching of metabolites and precursors and the data-driven identification methods, 32 chemicals were efficiently identified as key toxic substances as main contributors to explain the different transcriptome biological effects such as cellular component, development, and DNA damage related, including 15 industrial compounds, 7 PPCPs, 6 pesticides, and 4 natural products. This study avoids the process of structure elucidation of toxic metabolites and can trace them directly to the precursors based on MS spectra, providing a new idea for the identification of key toxic pollutants of metabolites.

Oxidative metabolism is impaired by phosphate deficiency during fracture healing and is mechanistically related to BMP induced chondrocyte differentiation

Prior studies of acute phosphate restriction during the endochondral phase of fracture healing showed delayed chondrocyte differentiation was mechanistically linked to decreased bone morphogenetic protein signaling. In the present study, transcriptomic analysis of fracture callus gene expression in three strains of mice was used to identify differentially expressed (FDR = q ≤ 0.05) genes in response to phosphate (Pi) restriction. Ontology and pathway analysis of these genes showed that independent of genetic background, a Pi-deficient diet downregulated (p = 3.16 × 10−23) genes associated with mitochondrial oxidative phosphorylation pathways as well as multiple other pathways of intermediate metabolism. Temporal clustering was used to identify co-regulation of these specific pathways. This analysis showed that specific Ox/Phos, tricarboxylic acid cycle, pyruvate dehydrogenase. Arginine, proline metabolism genes, and prolyl 4-hydroxylase were all co-regulated in response to dietary Pi restriction. The murine C3H10T½ mesenchymal stem cell line was used to assess the functional relationships between BMP2-induced chondrogenic differentiation, oxidative metabolism and extracellular matrix formation. BMP2-induced chondrogenic differentiation of C3H10T½ was carried out in culture media in the absence or presence of ascorbic acid, the necessary co-factor for proly hydroxylation, and in media with normal and 25 % phosphate levels. BMP2 treatment led to decreased proliferation, increased protein accumulation and increased collagen and aggrecan gene expression. Across all conditions, BMP2 increased total oxidative activity and ATP synthesis. Under all conditions, the presence of ascorbate further increased total protein accumulation, proly-hydroxylation and aggrecan gene expression, oxidative capacity and ATP production. Lower phosphate levels only diminished aggrecan gene expression with no other effects of metabolic activity being observed. These data suggest that dietary phosphate restriction controls endochondral growth in vivo indirectly through BMP signaling, which upregulates oxidative activity that is linked to overall protein production and collagen hydroxylation.

Pathogenetic role of intestinal microflora in carbohydrate malabsorption syndrome in early-aged children with rotavirus infection

The aim is to evaluate the effect of metabolic activity of intestinal microflora on laboratory manifestations of carbohydrate malabsorption syndrome in early-aged children with rotavirus infection by studying the main intestinal metabolites – short-chain fatty acids in faeces. Materials and methods. 60 breastfed children with rotavirus infection aged 1–24 months were examined. The total amount of carbohydrates in faecal samples was determined using Benedict’s test, and the detection of short-chain fatty acids in faeces was carried out using liquid chromatography in the dynamics of the disease – on the 3rd, 5th and 10th day. Results. It was established, that the amount of reducing sugars in faeces decreased with the increasing concentration of intestinal microflora metabolites during the entire period of rotavirus infection. In patients with ≤0.5 % level of carbohydrates in faeces, the total content of short-chain fatty acids was the highest and exceeded by 2.0, 1.8 and 1.7 times the indicators of children with Benedict’s test values >0.5 % on the 3rd, 5th and 10th days of the disease, respectively (p < 0.05). A decrease in the metabolic activity of the intestinal microbiota in the above category of children occurred mainly due to a deficiency in the production of acetic and propionic acids (P < 0.05). In the acute period of the disease, an imbalance in the intestinal microbiota infrastructure was noted towards a deficiency of obligate anaerobes that was expressed in a decrease in the anaerobic index (P < 0.05). The severity of these disorders influenced the severity of carbohydrate malabsorption: with an increase in the level of undigested sugars in faeces >0.5 %, the anaerobic index values were 3 and 5 times lower than at a carbohydrate level ≤0.5 % on the 3rd and 5th days of the disease, respectively (P < 0.05). Conclusions. It has been found that early-aged children with rotavirus infection have structural and functional disorders of the intestinal microflora, which influence the severity of carbohydrate malabsorption syndrome. The lower the saccharolytic activity of intestinal bacteria, the more pronounced the manifestations of this syndrome during the entire period of the disease.

The use of FISH-comet to detect c-Myc and TP 53 damage in extended-term lymphocyte cultures treated with terbuthylazine and carbofuran

Terbuthylazine and carbofuran are suspected to cause non-Hodgkin's lymphoma and lung cancer. We evaluated the effects of prolonged exposure to low concentrations on primary DNA damage by comet assay, and on the structural integrity of c-Myc and TP 53 genes by FISH-comet. Another novelty in studying these pesticides’ genotoxicity is the use of 14-day extended-term human lymphocyte cultures. Concentrations corresponded to values of ADI and OEL: for terbuthylazine 0.58ng/ml and 8ng/ml; for carbofuran 8ng/ml and 21.6ng/ml, respectively. A possible effect of metabolic activation (S9) was also considered. Carbofuran treatment induced a significant migration of DNA into the tail in a concentration-dependent manner, while for terbuthylazine the effect was significant only at the higher concentration. Terbuthylazine caused migration of both c-Myc signals into the comet tail. A significant occurrence of TP 53 signals in the tail was observed at 8ng/ml. Prolonged carbofuran treatment significantly elevated the migration of a single c-Myc signal into the tail in a concentration-dependent manner. With S9, distribution of signals shifted toward increased presence of both signals in tail. Our results showed impaired structural integrity of c-Myc and TP 53 due to prolonged exposure to terbuthylazine and carbofuran.

The impact of Triton WR-1339 induced hyperlipidemia on the effects of benzo(a)pyrene or guaiacol on α- and γ-tocopherol pools and selected markers of pro-/antioxidative balance in rat plasma and erythrocytes

The toxicity of carcinogenic benzo(a)pyrene (BaP) can be intensified by the pro-oxidative effects of metabolic activation. The oxidatively active products can be formed during enzymatic biotransformation or in the process of co-oxygenation with lipid peroxidation. This study assesses if the acute hyperlipidemia can increase pro-oxidative effects of BaP as a factor intensifying processes of lipid peroxidation and co-oxygenation. After three days of i.p. administration of BaP or guaiacol (equimolar dose 10mg/kg b.w.) without or with the hyperlipidemia inducer-Triton WR-1339 to male Wistar rats, the levels of α- and γ-tocopherol were measured in erythrocytes and plasma together with the level of lipid peroxidation as malonyldialdehyde (MDA) concentration. Guaiacol was chosen as a reference substance due to its high ability to co-oxygenate. Additionally, the activity of superoxide dismutase (Cu,ZnSOD) in erythrocytes and plasma was monitored. In normolipaemic groups the significant decrease in erythrocyte α-tocopherol pool and the increase in lipid peroxidation level were observed after BaP or guaiacol administration. In hyperlipaemic groups, despite the increase in the level of lipid peroxidation, there were no additional effects in tocopherol pools compared to the normolipaemic groups which could be attributed to co-oxygenation. Decrease of α-tocopherol in erythrocytes was proportional to the reduction in normolipemic subjects when accounting for the migration to hyperlipemic plasma. There was no co-oxygenation effect on the activity of superoxide dismutase (Cu,ZnSOD) in blood.

O2 uptake and muscle deoxygenation kinetics during the transition to moderate-intensity exercise in different phases of the menstrual cycle in young adult females

O(2) uptake (VO2) kinetics were examined during the follicular (F) and luteal (L) phases of the menstrual cycle to determine if there was an effect of altered sex hormones on the (VO2) response to moderate-intensity exercise. Seven healthy women (age 21 +/- 2 years; mean +/- SD) performed six transitions from 20 W to moderate-intensity exercise (approximately 90% theta L) during the F and L phase. VO2 was measured breath-by-breath and deoxyhemoglobin/myoglobin (Delta HHb) was determined by near infrared spectroscopy. Progesterone and estrogen were significantly (P < 0.05) elevated during the L compared to F phase. VO2 kinetics (tau VO2) were not different in the two phases of the menstrual cycle (F, 22 +/- 5 s; L, 22 +/- 6 s; 95% confidence intervals +/-4 s) nor was the time course of the Delta HHb response (F, TD 11 +/- 2 s, tau 11 +/- 3 s; L, TD 12 +/- 2 s, tau 12 +/- 11 s; tau HHb 95% confidence intervals +/-3 s). Respiratory exchange ratio (RER) was not different between phases for baseline or steady-state exercise and the blood lactate response to exercise was not different. In conclusion, VO2 kinetics at the onset of moderate-intensity exercise are not affected by the phase of the menstrual cycle in young females suggesting either no change in, or no effect of metabolic activation on the on-transient kinetics of moderate-intensity exercise. Additionally, the similar adaptation of Delta HHb in combination with unchanged VO2 suggests that there were no differences in the adaptation of local muscle O(2) delivery.

Differential oxidant potential of carcinogenic and weakly carcinogenic estrogens: Involvement of metabolic activation and cytochrome P450.

Different estrogens vary in their carcinogenic potential despite having similar hormonal potencies; however, mechanisms of estrogen-induced carcinogenesis remain to be fully elucidated. It has been hypothesized that generation of reactive estrogen-quinones and oxidative stress, both of which result from metabolic activation of estrogens, play an essential role in estrogen-induced carcinogenesis. This hypothesis was tested using the estrogen-receptor (ER)-alpha-positive hamster kidney tumor (H301) and the human breast cancer (MCF-7) cell lines. Estrogens with differing carcinogenic potentials were compared in terms of their capacities to induce 8-iso-prostaglandin F(2alpha) (8- iso-PGF(2alpha)), a marker of oxidative stress. Tumor cells were treated with either 17beta-estradiol (E2), a carcinogenic estrogen or 17-alpha-ethinylestradiol (EE), a weakly-carcinogenic estrogen. Tumor cells were also treated with alpha-naphthoflavone, a cytochrome P450 inhibitor, or a combination of alpha-naphthoflavone and E2 to study the effect of metabolic activation of E2 on E2-induced oxidative stress. H301 cells treated with E2 displayed time- and dose-dependent increases in 8-iso-PGF(2alpha), compared to controls; treatment with 10 nM E2 resulted in a maximal 4-fold induction following 48 h of treatment. In contrast, H301 cells treated with EE did not display an increase in 8-iso-PGF(2alpha) compared with controls. In H301 cells cotreated with alpha-naphthoflavone and E2, alpha-naphthoflavone inhibited the E2-induced increase in 8-iso-PGF(2alpha). These data indicate that a carcinogenic estrogen shows strong oxidant potential, whereas a weakly-carcinogenic estrogen shows poor oxidant potential. Furthermore, inhibiting metabolic activation of a carcinogenic estrogen blocks its oxidant potential. Our data support the hypothesis that metabolic activation and subsequent generation of oxidative stress may play critical roles in estrogen-induced carcinogenesis.

Preparation and characteristics of resting cells of bioluminescent Pseudomonas putida BLU

A bioluminescent strain, Pseudomonas putida BLU, which was created by inserting the lux gene into the chromosome of P. putida mt-2 (TOL), a well-known degrader for benzene, toluene and xylene (BTX), produces luminescence depending on both cell concentration and intracellular metabolic activity, including the intracellular level of reduced riboflavin phosphate (FMNH 2). To estimate the cell concentration of a BTX degrader by the rapid detection of bioluminescence in a bioaugmentation system, the effect of metabolic activity on the output of bioluminescence needs to be considered. For this purpose, the preparation of resting cells of P. putida BLU, defined as incapable of growing but having metabolic activity, was tried using different surfactants. Resting cells formed on addition of n-dodecyltrimethylammonium bromide (DTAB, a cationic surfactant) at a concentration below the critical micellar concentration (CMC) to the bacterial culture, and exhibited morphological change. The P. putida BLU showed a decrease in bioluminescence output to a constant level and stopped growing immediately after the addition of DTAB, while maintaining activity for oxygen consumption. When the bacterial culture treated with DTAB was washed with a 0.9% saline solution, the growth and bioluminescence of the resting cells recovered to the normal level. The bioluminescence output (LUX) of the resting cells prepared at different time points from the bacterial culture correlated only with the cell concentration ( X), LUX∝ X 1.0, suggesting that generating resting cells enables the cell concentration to be simply and rapidly quantified by measuring the luminescence.

Inter-individual variation of smoking-related DNA adducts in lymphocytes-relationship to mRNA levels for CYP1A1 and DNA repair enzymes

The measurement of DNA adducts is a useful indicator for environmental carcinogen exposure monitoring. To clarify the effect of metabolic activation and DNA repair system on the inter-individual variation of DNA adduct levels, aromatic DNA adducts and mRNA expression of metabolic and repair enzymes were measured in 43 human lymphocytes. Aromatic DNA adducts were measured by the nuclease P1 postlabelling method. The metabolic activation enzyme; cytochrome P4501A1 (CYPIA1), and the repair enzyme; excision repair cross complimenting gene (ERCC1), and the xerodermapigmentosum C group cell gene (XPCC), mRNA expression were measured by thereverse transcription-PCR method. The mean adduct levels were 1.01 ± 0.49 in 43 subjects. There was a positive correlation between DNA adducts and CYP1A1 mRNA (r = 0.33, p = 0.12). DNA adduct levels had a positive correlation with ERCC1 (r = 0.35, p = 0.03) and a negative correlation with XPCC mRNA levels (r = –0.28, p = 0.07). We found Brinkman index, CYP1A1 genotypes, CYP1A1 mRNA and XPCC mRNA as a predictor for log DNA adduct levels in multivariate analysis. Metabolic activation and the repair system may explain the inter-individual variation of DNA adducts in lymphocytes.

The relationship between microbial metabolic activity and biocorrosion of carbon steel

The effect of metabolic activity (expressed by generation time, rate of H2S production and the activity of hydrogenase and adenosine phosphosulphate (APS)-reductase enzymes) of the 8 wild strains of Desulfovibrio desulfuricans and of their resistance to metal ions (Hg2+, Cu2+, Mn2+, Zn2+, Ni2+, Cr3+) on the rate of corrosion of carbon steel was studied. The medium containing lactate as the carbon source and sulphate as the electron acceptor was used for bacterial metabolic activity examination and in corrosive assays. Bacterial growth inhibition by metal ions was investigated in the sulphate-free medium. The rate of H2S production was approximately directly proportional to the specific activities of the investigated enzymes. These activities were inversely proportional to the generation time. The rate of microbiologically induced corrosion (MIC) of carbon steel was directly proportional to bacterial resistance to metal ions (correlation coefficient r = 0.95). The correlation between the MIC rate and the activity of enzymes tested, although weaker, was also observed (r = 0.41 for APS-reductase; r = 0.69 for hydrogenase; critical value rc = 0.30, p = 0.05, n = 40).

Metabolic activation of nitrodibenzofurans by rat liver in Salmonella/mutagenicity test

The effect of metabolic activation on the mutagenicity of nitrodibenzofurans (NDF) by rat liver S9 was evaluated with S. typhimurium tester strains. Except for 1-nitrodebenzofuran (NDF), five tested NDFs were mutagenic in strains TA98 and TA98/1,8-DNP 6 without S9 mix but were not mutagenic in strain TA98NR. NDFs mutagenized strain TA98NR with S9 mix, and the NAD(P)H system plus 3-methylcholanthrene-induced S9 (3-MC-S9) was the most effective. The specificity of S9 enzyme(s) participating in the activation of NDFs was different from that of endogenous enzyme(s) in strain TA98, i.e., the order of mutagenic potency of NDFs in strain TA98 without S9 mix was 2,8-=2,7→3→2→4→1-nitrated dibenzofuran and 2-NDF and 2,8-dinitrodibenzofuran (DNDF) were more mutagenic than 3-NDF and 2,7-DNDF, respectively, strain TA98NR with S9 mix. The mutagenic potency of 2-NDF, 4-NDF, 2,7-DNDF and 2,8-DNDF in strain TA98NR with S9 mix was stronger than those in strain TA98 without S9 mix and the cytosolic fraction of the 3-MC-S9 accounted for more of the activation than the microsomal fraction. Studies with electron donors and inhibitors indicated that xanthine oxidase and/or NAD(P)H-quinone oxido-reductase (NQOR) participated in the activation of NDFs. The mutagenic potency of NDFs in strain TA98NR with S9 mix (3-MC-S9) was reflected in the induction of NQOR by pretreatment of rats with 3-MC.

Einfluß der Ernährungslage auf das31P-MR-Spektrum der gesunden Leber

Previous investigations in animal and human liver spectroscopy revealed a strong effect of metabolic activity on the 31P-spectra of the liver. This study examined the influence of a standardised meal on the liver spectra of healthy volunteers. The measurements were performed at 1.5 T (Magnetom, Siemens). The results show that the metabolic condition has a strong effect on the 31P MR liver spectra. The changes are of the same order of magnitude as those described in spectra of focal or diffuse liver diseases. This indicates that identical metabolic conditions are necessary for measuring liver spectra of volunteers and patients, especially in follow-ups.

Evaluation of the developmental toxicity of five compounds with the frog embryo teratogenesis assay: Xenopus (FETAX) and a metabolic activation system.

The potential teratogenic hazard of five compounds was evaluated using the Frog Embryo Teratogenesis Assay--Xenopus (FETAX) and a metabolic activation system. Embryos of the South African clawed frog, Xenopus laevis, were exposed to (i) three compounds suspected to be proteratogenic in mammalian test systems--[2-acetylaminofluorene (2-AAF), rifampicin (RA) and benzo[a]pyrene (BP)] for 96 h; (ii) one compound unaffected by mixed-functional oxidase (MFO) metabolism--ZnSO4; (iii) one compound thought to be inactivated by cytochrome P-450--cytochalasin D (CD). Two separate static renewal tests were conducted with and without the presence of an exogenous metabolic activation system (MAS). The metabolic activation system consisted of Aroclor 1254-induced rat liver microsomes. The teratogenic potential of each compound and the effects of metabolic activation were based on teratogenic indices [TI = 96 h LC50/96 h EC50 (malformation)], types and severity of malformation, and effects on embryo growth. Metabolic activation increased the potential teratogenic hazard of 2-AAF, RA and BP by TI factors of 1.3, 2.8 and 6.8, respectively. The teratogenic potential of ZnSO4 was virtually unaffected by the MAS. The MAS significantly reduced the teratogenic potential of CD by a TI factor of 2.7. These results demonstrate the utility and importance of a MAS for in vitro developmental toxicity screens such as FETAX. Consistent use of a MAS with FETAX should reduce the number of potential false-positive and false-negative test results.

Cholinesterase inhibition by organophosphorus and carbamate pesticides in aggregate cultures of neural cells from the foetal rat brain: The effects of metabolic activation and pesticide mixtures

The effects of pesticide mixtures on cholinesterase activity in aggregate cultures of neural cells were investigated; we also determined whether exogenous rat-liver microsomal fraction (S-9) might be used in conjunction with the cultures to mimic the in vivo activation of pesticides such as malathion. Studies of the effects of pesticide mixtures on the cholinesterase activity of cultures demonstrated that a hepatic microsomal fraction (S-9) played a major role in the nature of the interaction between combinations of malathion and fenitrothion or carbofuran. In the absence of S-9, malathion potentiated the anti-cholinesterase effect of fenitrothion, while neither synergistic nor antagonistic interactions occurred with mixtures of carbofuran and malathion. When S-9 was added to cultures with the pesticide mixtures, malathion's interaction with fenitrothion was antagonistic, and a synergistic response was observed for the mixtures of malathion and carbofuran. The antagonistic interaction of mixtures of fenitrothion and carbofuran was demonstrated to be independent of exogenously added S-9. Neither antagonistic nor synergistic interactions were observed for mixtures of triallate and fenitrothion or carbofuran. The data indicate that the addition of exogenous S-9 may be used to mimic certain aspects of the in vivo biotransformation of pesticides in aggregate cultures of neural cells from rat brain. Furthermore, the effects on cholinesterase activity of several of the pesticide mixtures tested were dependent upon the presence of exogenous S-9.

The effects of metabolic activation on the mutagenicity of aminoacridines.

The mutagenic activity of a series of aminoacridines was examined by the preincubation method with and without mammalian metabolizing enzymes in Salmonella tester strains. Without metabolizing enzymes, three acridines having an amino substituent at position 9 showed high activity in Salmonella typhimurium TA1537 and TA1977, and other acridines with amino substituents at position 2 or 3 were mutagenic but were less effective than the 9-aminoanalogs. The liver microsomal enzymes generally deactivated acridine mutagenicity in TA1537, but created a broad spectrum of mutagenicity if tested by the reversion of TA1535, the strain detecting base-pair substitution mutagens, and TA 1538, the strain detecting covalently bound frameshift mutagens.

Production of frameshift mutations in Salmonella by phenanthridinium derivatives: enzymatic activation and photoaffinity labeling

The effect of metabolic activation on the mutagenic potential of some phenanthridinium compounds was examined in Salmonella typhimurium strains TA1538 and TA1978. All of the compounds tested were mutagenic in TA1538, a DNA excision-repair-deficient strain, when metabolizing enzymes were included in the assay. Reversions were not detected when these compounds were examined under the same conditions in TA1978, the isogenic strain of TA1538 proficient in DNA repair. The mutagenic activity of an azido analog of propidium iodide was also examined using photoactivation and enzymatic activation, and with both conditions, reversions were observed in TA1538 but not in TA1978. Furthermore, the ranking of mutagenic activity of propidium azide relative to ethidium azide analogs was comparable for both types of activation. The evidence from several studies suggests that the structural requirements for mutagenic activity for this series of phenanthridinium compounds appear to be the same whether mutagenesis is induced via photoactivation or metabolic activation. The interaction with DNA resulting in covalent alteration of the DNA is implicated as the mutagenic mechanism whether the active species is generated by metabolic- or photo-activation.

The use of XAD-resins for the detection of mutagenic activity in water: II. Studies with drinking water

The combined XAD-4/8-Ames test procedure for concentrating and detecting trace amounts of organic mutagens, as already described for surface water, is shown to be suitable for drinking water as well. DMSO is as effective as acetone in eluting the adsorbed mutagens, and optimal recovery of overall mutagenic activity is observed at a flow rate of 2–4 bed volumes/min. The drinking water of 6 cities in The Netherlands, which prepare their drinking water from the rivers Rhine and Meuse, has been tested for mutagenic activity. Mutagenic activity could be demonstrated in 4 cities. Dose-related responses are observed with concentrates of as little as 500 ml of drinking water and the 4 cities clearly differ with regard to the type of mutations induced (TA 98 or TA 100) and the effect of metabolic activation. The absence of mutagenic activity in drinking water of 2 cities indicates that by a proper combination of treatment processes the organics which are responsible for the detected mutagenic activity in drinking water can be removed to a high degree.

The effect of metabolic activation with rat liver preparations on the mutagenicity of several N-nitrosamines on a streptomycin-dependent strain of Escherichia coli

Summary The mutagenicity of dimethyl, diethyl, di- n -propyl, di- n -butyl, methyl- n -butyl, morpholine, piperidine, methylphenyl, ethyl- t -butyl and diphenyl nitrosamines was investigated using a mammalian metabolic activation system. Reverse mutation from streptomycin dependence to non-dependence in strain Sd-B(TC) of Escheyichia coli was used as the marker for mutagenicity. With this assay system the mutagenicity of metabolic breakdown products was determined by incubating the compounds with a rat liver preparation in the presence of bacterial cells. Reverse mutation was induced by all carcinogenic compounds tested, except methylphenylnitrosamine, whereas two non-carcinogenic compounds, ethyl- t -butyl nitrosamine and diphenyl nitrosamine did not give a significant increase in the rever sion frequency. The frequency of mutants induced by the compounds was decreased markedly by preincubation of the compounds with the liver preparation and the cofactor system prior to the addition of bacterial cells.

Effect of metabolic activity on the glucose permease of bacterial cells.

Abstract : The experiments all point to a difference be tween the glucose (alpha methyl glucoside) ac cing system of both S. typhimurium and E. coli and the beta-galactoside and galatose ac cumulating systems of E. coli. Active respira tory activity accompanied by oxidative phosphory lation depresses rather than enhances the steady state level of alpha MG accumulated within the cells. The level attained during the oxidation of an exogenously supplied substrate can be raised by the addition of dinitrophenol or azide at suitable concentrations. Furthermore, the alpha MG accumulation is greater when the cells depend for their energy supply on endogenous respiration or on the anaerobic fermentation of an exogenous substrate rather than on the active oxidation of such a substrate in the absence of poisons. (Author)

Recovery from X-Ray-Induced Sensitivity to Heat in an Insect

In recent studies of the interaction of heat and X-radiation in killing an insect (1), it has been demonstrated that the amount of killing depends on the order in which the two kinds of exposure occurred. When a sublethal dose of heat preceded a sublethal dose of X-radiation, killing was neglibible. When the exposures were given in the reverse order, however, the majority of the insects were dead within 24 hours. Thus, the X-rays seemed to sensitize the insects to a subsequent heat exposure. Later work indicated that this sensitizing effect would partially disappear with increasing time between the X-radiation and the heat exposures. This paper is concerned with the recovery of Dahlbominus fuscipennis (Zett.) from X-ray-induced sensitivity to heat, and the effects of metabolic activity on the rate of this