Extremely low frequency magnetic fields affect transposition activity in Escherichia coli

The aim of this study was to verify whether extremely low frequency (ELF) magnetic fields (MF) could affect transposition activity like some environmental stress factors such as heat shock or UV irradiation. Using an Escherichia coli Lac Z(-) strain transformed with a plasmid containing a Tn 10 derivative element expressing beta-galactosidase only after transposition, it was possible to determine the events of transposition evaluating the rate at which the colonies developed dark coloured papillae (Lac Z(+)). We found that those bacteria that had been exposed for a long time (58 h) to a 50 Hz low intensity MF (0.1-1 mT) gave colonies with significantly lower transposition activity compared to sham-exposed bacteria. Such reduction in transposition activity was positively correlated to the intensity of the MF, in a dose-effect manner. This phenomenon was not affected by bacterial cell proliferation, since no significant differences were observed in number, diameter and perimeter between sham-exposed and MF-exposed colonies.     

I87E mutation prevents barstar dimerization

The C40,82A;I87E mutant of barstar, an intracellular inhibitor of the ribonuclease barnase from Bacillus amyloliquefaciens, was obtained, and its physicochemical properties were studied. It was produced as a fusion protein with thioredoxin and then cleaved from this by EKmax enterokinase. The mutant was shown by NMR to retain the spatial structure of the wild-type protein but, in contrast to barstar, does not form the homodimers characteristic of barstar in aqueous solution. The mutant protein binds barnase with the dissociation constant (6.6 +/- 1.1) x 10(-11) M and exhibits other physicochemical properties similar to those of the wild-type barstar. This allows the use of C40,82A;I87E mutant instead of wild-type barstar in investigations where the protein dimerization is undesirable. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 6; see also http://www.maik.ru.     

Drug failure during HIV-1 treatment. New perspectives in monitoring drug resistance

Since the discovery of 3'-azido-3'deoxthymidine (zidovudine) as an effective antiretroviral agent against human immunodeficiency virus type 1 (HIV-1), drug therapy has been widely used in the treatment of AIDS. To date, new combination therapies have significantly altered the longterm prognosis for HIV-infected patients showing a reduction of plasma viral load, associated with clinical and immunological recovery. Nevertheless, in various circumstances treatment can fail for several reasons, such as patient noncompliance with the therapeutic regimen, suboptimal antiviral drug concentrations, drug pharmacokinetics, and virus resistance to one or more drugs. Virus drug resistance is the most important factor contributing to the failure of antiretroviral therapy. Since some evidence indicates that viral resistance and treatment failure are closely linked, this brief review explores the routine determination of drug resistance and its importance to shed more light on the meaning of mutations correlated to drug resistance.     

Effects of food processing on flavonoids and lycopene status in a Mediterranean tomato variety

This research is focused on the antioxidant properties of dietary components, in particular phenolics and carotenoids and the assessment of the contribution of the combined antioxidants to the total antioxidant activity (TAA) of tomato fruit. The aim of this study was to analyse the effects of processing on the antioxidant properties of tomato. The effects of three different methods of processing fresh tomatoes into tomato sauce were investigated with respect to the antioxidant properties of the fruit. Identification and quantification of the main carotenoids and flavonoids present in tomatoes was achieved by HPLC analysis and the effect on the concentration and availability of these compounds was investigated at different stages of the processing. The processing affected mainly naringenin causing a reduction in the concentration. Conversely, levels of chlorogenic acid were increased suggesting an improvement in availability of this compound to extraction. The concentration of all- trans -lycopene was also increased following processing. Less than 10% isomerisation of all- trans -lycopene to the cis form was detected for all the methods analysed. The effects of processing on the overall antioxidant activity support the theory of a general improvement in availability of individual antioxidants. For both hydrophilic and lipophilic extracts TAA values were increased.     

Assessing human impact despite uncertainty:viability of the northern spotted owl metapopulation in the northwestern USA

We demonstrate the effect of uncertainty (resulting from lack of information or measurement error) on the assessment of human impact, with an analysis of the viability of the northern spotted owl throughout its range in the United States. We developed a spatially-explicit, stage-structured, stochastic metapopulation model of the northern spotted owl throughout its range in the United States. We evaluated the viability of the metapopulation using measures such as risk of decline and time to extinction. We incorporated uncertainty in the form of parameter ranges, and used them to estimate upper and lower bounds on the estimated viability of the species. We analysed the effect of this type of uncertainty on the assessment of human impact by comparing the species' viability under current conditions and under an assumed loss of spotted owl habitat in the next 100 years. The ranges of parameters were quite large and resulted in a wide range of risks of extinction. Despite this uncertainty, the results were sensitive to parameters related to habitat loss: under all assumptions and combinations of parameters, the model predicted that habitat loss results in substantially higher risks of metapopulation decline. This result demonstrated that even with relatively large uncertainties, risk-based model results can be used to assess human impact reliably.     

Kinetics of CheY phosphorylation by small molecule phosphodonors.

The chemotaxis response regulator CheY can acquire phosphoryl groups either from its associated autophosphorylating protein kinase, CheA, or from small phosphodonor molecules such as acetyl phosphate. We report a stopped-flow kinetic analysis of CheY phosphorylation by acetyl phosphate. The results show that CheY has a very low affinity for this phosphodonor (K(s)&z.Gt;0.1 M), consistent with the conclusion that, whereas CheY provides catalytic functions for the phosphotransfer reaction, the CheA kinase may act simply to increase the effective phosphodonor concentration at the CheY active site.     

Lack of mechanism-based inactivation of rat hepatic microsomal cytochromes P450 by doxorubicin.

Administration of the antineoplastic doxorubicin to rodents causes depression of hepatic cytochrome P450 (CYP) dependent biotransformation, an effect that has been partially attributed to the ability of doxorubicin to stimulate microsomal lipid peroxidation. Since doxorubicin can be bioactivated by the CYP/NADPH-CYP reductase system to products that bind covalently to microsomal protein, we hypothesized that doxorubicin functions as a mechanism-based inactivator of hepatic microsomal CYPs and (or) NADPH-CYP reductase under conditions in which doxorubicin-stimulated NADPH-dependent lipid peroxidation is minimized. In vitro studies were conducted with hepatic microsomes isolated from untreated and phenobarbital-treated male rats. Unlike the positive control carbon tetrachloride, doxorubicin (10 microM) did not stimulate NADPH-dependent lipid peroxidation in microsomal incubations containing EDTA (1.5 mM). Doxorubicin did not cause NADPH-dependent loss of microsomal CYP, heme, or steroid hydroxylation activities selective for CYP2A, CYP2B, CYP2C11, and CYP3A. The positive control 1-aminobenzotriazole caused marked NADPH-dependent decreases in all of these parameters. Neither doxorubicin nor 1-aminobenzotriazole caused NADPH-dependent loss of NADPH-CYP reductase activity, and neither compound altered the immunoreactive protein levels of CYP2B, CYP2C11, CYP3A, and NADPH-CYP reductase. These results indicate that a pharmacologically relevant concentration of doxorubicin does not cause direct mechanism-based inactivation of hepatic microsomal CYPs or NADPH-CYP reductase, suggesting that the ability of doxorubicin to depress hepatic CYP-mediated biotransformation in vivo is due to lipid peroxidation mediated heme destruction, altered heme metabolism, and (or) decreased expression of selected CYP enzymes.     

Various effects on transposition activity and survival of Escherichia coli cells due to different ELF-MF signals

Previous assays with weak sinusoidal magnetic fields (SMF) have shown that bacteria that had been exposed to a 50 Hz magnetic field (0.1–1 mT) gave colonies with significantly lower transposition activity as compared to sham-exposed bacteria. These experiments have now been extended by using a pulsed-square wave magnetic field (PMF) and, unexpectedly, it was found that bacteria exposed to PMF showed a higher transposition activity compared to the controls. The increase of the transposition activity was positively correlated with the intensity of the magnetic fields (linear dose-effect relation). This phenomenon was not affected by any bacterial cell proliferation, since no significant difference was observed in number and size of PMF-exposed and sham-exposed colonies. In addition, the cell viability of E. coli was significantly higher than that of the controls when exposed to SMF, and lower than that of the controls when exposed to PMF. Under our experimental conditions it was shown that exposure to PMF stimulates the transposition activity and reduces cell viability of bacteria, whereas exposure to SMF reduces the transposition mobility and enhances cell viability. These results suggest that the biological effects of magnetic fields may critically depend on the physical characteristics of the magnetic signal, in particular the wave shape.     

The verification of the results of screening antibodies to hepatitis C virus in blood donors

6,744 persons were examined for the presence of antibodies to hepatitis C virus (HCV) before blood donation (4,219 persons in Moscow and 2,525 persons in St. Petersburg). The serum samples found to contain antibodies to HCV were additionally studied by the immunoblot techniques. The positive results of antibody screening were registered in 78 persons: 26 persons in Moscow (0.62%) and 52 in St. Petersburg (2.05%). In both cities the positive results of screening were confirmed in 62% of cases. Different occurrence of the profile with the presence of antibodies to all fragments of the virus: 52% in Moscow, 12% in St. Petersburg (chi2 = 12.11; p < 0.001). Considerable differences were also registered in the spread of individual antibodies.