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801.
Surinder S. Deo Romesh Saini Roswell S. Coles Raghbir S. Athwal 《Biochimica et Biophysica Acta (BBA)/General Subjects》1985,839(3):233-239
The enzyme xanthine-guanine phosphoribosyltransferase from scherichia coli cells harboring the plasmid pSV2gpt has been purified 30-fold to near homogeneity by single-step GMP-agarose affinity chromatography. It has a Km value of 2.5, 42 and 182 μM for the substrates guanine, xanthine and hypoxanthine, respectively, with guanine being the most preferred substrate. The enzyme exhibits a Km value of 38.5 μM for PRib-PP with guanine as second substrate and of 100 μM when xanthine is used as the second substrate. It is markedly inhibited by 6-thioguanine, GMP and to a lesser extent by some other purine analogues. Thioguanine has been found to be the most potent inhibitor. The subunit molecular weight of xanthine-guanine phosphoribosyltransferase was determined to be 19 000. The in situ activity assay on a nondenaturing polyacrylamide gel electrophoresis gel has indicated that a second E. coli phosphoribosyltransferase preferentially uses hypoxanthine as opposed to guanine as a substrate, and it does not use xanthine. 相似文献
802.
Microbial survival in mineralizing environments depends on the ability to evade surface encrustation by minerals, which could obstruct nutrient uptake and waste output. Some organisms localize mineral precipitation away from the cell; however, cell surface properties – charge and hydrophobicity – must also play a role in preventing surface mineralization. This is especially relevant for iron‐oxidizing bacteria (FeOB), which face an encrustation threat from both biotic and abiotic mineralization. We used electron microscopy and surface characterization techniques to study the surfaces of two stalk‐forming neutrophilic FeOB: the marine Zetaproteobacterium Mariprofundus ferrooxydans PV‐1 and the recently isolated freshwater Betaproteobacterium Gallionellales strain R‐1. Both organisms lack detectable iron on cell surfaces. Live and azide‐inhibited M. ferrooxydans PV‐1 cells had small negative zeta potentials (?0.34 to ?2.73 mV), over the pH range 4.2–9.4; Gallionellales strain R‐1 cells exhibited an even smaller zeta potential (?0.10 to ?0.19 mV) over pH 4.2–8.8. Cells have hydrophilic surfaces, according to water contact angle measurements and microbial adhesion to hydrocarbons tests. Thermodynamic and extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) calculations showed that as low charge causes low electrostatic attraction, hydrophilic repulsion dominates cell–mineral interactions. Therefore, we conclude that surface properties help enable these FeOB to survive in highly mineralizing environments. Given both mineral‐repelling surface properties and the ability to sequester Fe(III) biominerals in an organomineral stalk, these two FeOB have a well‐coordinated system to localize both biotic and abiotic mineral distribution. 相似文献
803.
Cytotechnology - Microglia has been reported to be able to regulate the proliferation, differentiation and survival of adult neural stem/progenitor cells (NSPCs) by modulating the microenvironment,... 相似文献
804.
The naturally occurring free and glycosylated flavans are reviewed. The distribution, methods of isolation and structure elucidation of flavans, by comprehensive spectral analyses, are presented. Biological properties of flavans are appraised. 相似文献
805.
Cluster Computing - The MapReduce (MR) scheduling is a prominent area of research to minimize energy consumption in the Hadoop framework in the era of green computing. Very few scheduling... 相似文献
806.
807.
Agricultural ornithology aims at obtaining scientific information on birds in relation to agriculture and using this information
for their management. Most of bird species play a useful role in agriculture by having a potent check on insect and rodent
pests. However, some granivorous bird species, having adapted to the agricultural habitats and increased in numbers, are conflicting
with our goals of agricultural production by inflicting economic losses to crops, fruits and stored grains. Bird management
involves both the conservation of useful species and control of pests. Agricultural ornithology is of special importance in
predominantly agricultural countries like India. Although a good deal of work has been done in this discipline in India, a
lot remains to be done and, in fact, the discipline is still in its infancy. This paper reviews the progress made in agricultural
ornithology in India, points out important problems and gaps in knowledge, and suggests approaches for future research. 相似文献
808.
809.
S. Saini W. Surareungchai A. P. F. Turner M. E. A. Downs 《Biosensors & bioelectronics》1995,10(9-10):945-957
This work investigates the feasibility of constructing a bioelectrochemical sensor that can operate directly in gases. A series of experiments are described, resulting in a sensor that is responsive to phenol vapours. The sensor was based on ionically conducting films that incorporate a biological redox catalyst at the surface of an array of interdigitated microband electrodes. Exposure to phenol vapour drives the bioelectrochemical reaction, providing a basis for a current signal under constant potential conditions. Ionic materials included Nafion and films based on tetrabutylammonium toluene-4-sulphonate (TBATS). The quasi-reversible electrode reaction of potassium hexacyanoferrate (II) within TBATS was investigated as a function of drying time. Eo′ and K0 were determined at a TBATS modified microdisc electrode under steady-state conditions. Drying time (water loss) from the TBATS film had the effect of increasing the film ionic strength. It was shown that as the film ionic strength increased, E0′ for potassium hexacyanoferrate (II) shifts toward positive potentials (because of ion pairing) and there was a corresponding increase in the heterogeneous rate constant K0. The latter effect was attributed to increasing ion-ion (cation-ferrocyanide ion) interactions as the film dried and the enhancing effect this had on the prevention of surface poisoning reactions at the electrode. These factors are discussed in relation to sensor design. 相似文献
810.