Glutathione S‐transferases (GSTs) belong to a family of detoxification enzymes that conjugate glutathione to various xenobiotics, thus facilitating their expulsion from the cell. GST activity is ...elevated in many insecticide‐resistant insects, including the DDT‐resistant malaria vector Anopheles gambiae. Crystals of the recombinant form of a GST from A. gambiae, agGST1‐6, have been grown in at least five different crystal forms, with a broad range of diffraction resolution limits. A complete 2.0 Å data set has been collected on a C‐centered orthorhombic crystal form with unit‐cell parameters a = 99.0, b = 199.4, c = 89.6 Å. A search for heavy‐atom derivatives has been initiated, along with phase‐determination efforts by molecular replacement.
Aflatoxin B1(AFB1) has been postulated to be a hepatocarcinogen in humans, possibly by causing p53 mutations at codon 249. AFB1is metabolized via the phase I and II detoxification pathways; hence, ...genetic variation at those loci may predict susceptibility to the effects of AFB1. To test this hypothesis, genetic variation in two AFB1detoxification genes, epoxide hydrolase (EPHX) and glutathione S-transferase M1 (GSTM1), was contrasted with the presence of serum AFB1-albumin adducts, the presence of hepatocellular carcinoma (HCC), and with p53 codon 249 mutations. Mutant alleles at both loci were significantly overrepresented in individuals with serum AFB1-albumin adducts in a cross-sectional study. Mutant alleles of EPHX were significantly overrepresented in persons with HCC, also in a case-control study. The relationship of EPHX to HCC varied by hepatitis B surface antigen status and indicated that a synergistic effect may exist. p53 codon 249 mutations were observed only among HCC patients with one or both high-risk genotypes. These results indicate that individuals with mutant genotypes at EPHX and GSTM1 may be at greater risk of developing AFB1adducts, p53 mutations, and HCC when exposed to AFB1. Hepatitis B carriers with the high-risk genotypes may be an even greater risk than carriers with low-risk genotypes. These findings support the existence of genetic susceptibility in humans to the environmental carcinogen AFB1and indicate that there is a synergistic increase in risk of HCC with the combination of hepatitis B virus infection and susceptible genotype.
An oxygen-evolving, Photosystem II particle was isolated from the thermophilic, blue-green alga,
Phormidium laminosum, according to the procedure of Stewart and Bendall (Stewart, A.C. and Bendall, D. ...(1979) FEBS Lett. 107, 308–312). Our particle has an oxygen-evolution activity of 1500–1600 μmol O
2/mg chlorophyll per h. The oxygen-evolution activity has a pH optimum at 5–6, and is abolished at pH 9. Maximum oxygen evolution occurs at approx. 47°C in whole cells, but at 29°C in the particles. The activity decreases to 50% when the cells are heated for 30 min at 55°C; with the particles, 50% inactivation occurred at 47°C for the same heating time of 30 min. Flash excitation of the particle at 100 K produced absorbance changes whose difference spectrum in the ultraviolet-to-near infrared region shows photochemical charge separation and recombination of P-680
+ and Q
− in the dark with
t
1
2
of 1.75 ms. An EPR spectrum for the P-680
+ free radical, with g 2.0027 and
ΔH
pp = 8 G, was constructed from flash-induced EPR changes under conditions identical to those used for obtaining P-680 absorbance changes. The actinic light-induced variable fluorescence yield is 5-fold that induced by the weak probing beam alone. Addition of dithionite to the particle brings the fluorescence to the same maximum level. Under the reducing condition, strong actinic light caused the fluorescence to decrease. This observation is consistent with the notion that variable fluorescence yield in Photosystem II originates, as in green-plant chloroplasts, from recombination luminescence, the attenuation of which corresponds to photoaccumulation of reduced pheophytin under these conditions. Broad segments (300 nm) of the difference spectrum for pheophytin photoreduction were recorded by an intensified photodiode array in conjunction with a phosphoroscopic photometer. Kinetic spectrophotometric assays together with chemical analysis showed a rather clean and simple stoichiometry in these particles, namely, 1 P-680:1 Ph:1 Q:4 Mn:44 Chl. Initial investigation failed to reveal the doublet EPR spectrum previously observed for Ph
−·Q
− Fe in spinach subchloroplast particles (Klimov, V.V., Dolan, E. and Ke, B. (1980). FEBS Lett. 118, 97–100). A hyperfine EPR spectrum consisting of 16–20 lines and presumably associated with the manganese clusters in the oxygen-evolving protein has been confirmed in these particles. Tris washing but not washing with EDTA eliminates this signal. Active oxygen-evolving particles also yield the II
vf signal with a
t
1
2
of approx. 800 μs. Upon Tris washing, the II
f signal appears which decays in 23.5 ms.
There is a growing demand for provisioning of different levels of quality of service (QoS) on scalable Web servers to meet changing resource availability and satisfy different client requirements. ...The proportional differentiation model is getting momentum because of its fairness and differentiation predictability. It states that QoS of different traffic classes should be kept proportional to their pre-specified differentiation parameters, independent of the class loads. In this paper, we present a processing rate allocation scheme for providing proportional response time differentiation on Web servers. A challenging issue is how to achieve processing rates for different request classes in the implementation. We propose a process allocation strategy, which dynamically and adaptively changes the number of processes allocated for handling different request classes while ensuring the ratios of process allocation specified by the processing rate allocation scheme. We implement the process allocation strategy at application level on Apache Web servers. Experimental results show that the processing rate can be achieved by the adaptive process allocation strategy and the Web servers can provide predictable and controllable proportional response time differentiation.
An air–soil layer coupled scheme is developed to compute surface fluxes of sensible heat and latent heat from data collected at the Oklahoma Atmospheric Radiation Measurement–Cloud and Radiation ...Testbed (ARM–CART) stations. This new scheme extends the previous variational method of Xu and Qiu in two aspects: 1) it uses observed standard deviations of wind and temperature together with their similarity laws to estimate the effective roughness length, so the computed fluxes are nonlocal; that is, they contain the contributions of largeeddy motions over a nonlocal area ofO(100 km²); and 2) it couples the atmospheric layer with the soil–vegetation layer and uses soil data together with the atmospheric measurements (even at a single level), so the computed fluxes are much less sensitive to measurement errors than those computed by the previous variational method. Surface skin temperature and effective roughness length are also retrieved as by-products by the new method.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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