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81.
In a continuous fermentation, significant advantages may be gained by immobilization of microbial cells. Immobilization allows cells to be retained in the fermenter or to be readily recovered and recycled. Therefore, the hydraulic retention time and the biomass retention time are decoupled. A novel cell immobilization has been developed for the immobilization of autotrophic bacteria by coculture with floc-forming heterotrophic bacteria with growth of the latter limited by the availability of organic carbon. The result is an immobilization matrix which grows along with the immobilized autotroph. We have previously demonstrated the utility of this approach by immobilizing the chemoautotroph Thiobacillus denitrificans in macroscopic floc by coculture with floc-forming heterotrophs from an activated sludge treatment facility. Floc with excellent settling characteristics were produced. These floc have now been used to remove H(2)S from a gas stream bubbled through continuous cultures. The stoichiometry and kinetics of H(2)S oxidation by immobilized T. denitrificans were comparable to that reported previously for free-cell cultures. Oxygen uptake measurements indicated the growth of both T. denitrificans and the heterotrophs although the medium contained no added organic carbon. Continuous cultures with total biomass recycle were maintained for up to four months indicating the long-term stability of the commensal relationship between the immobilized autotroph and the heterotrophs which composed the immobilization matrix. It was observed that at any given H(2)S loading the biomass concentration reached a maximum and leveled out. The ultimate biomass concentration was dependent upon the H(2)S feed rate. 相似文献
82.
G. M. Shah U. C. Goswami R. K. Bhattacharya 《Journal of biochemical and molecular toxicology》1992,7(3):177-181
Several vitamin A compounds have been tested for their ability to suppress formation of DNA adduct by the carcinogen benzo[a]pyrene (B[a]P) in an in vitro reaction catalyzed by rat liver microsomes. Retinol, retinal, 3-dehydroretinol and 3-hydroxyretinol were found to be effective inhibitors of adduct formation. Certain carotenoids that are precursors of these retinoids also displayed considerable inhibitory capacity. Carotenoids and the 3-substituted retinoids appeared to modulate the DNA adduct formation exclusively through their action on microsomal enzymes, since an effective inhibition in each case was observed on the formation of B[a]P-7,8-diol, a proximate carcinogenic metabolite of B[a]P. Unsubstituted retinoids, on the other hand, had marginal effect on enzymes but were found effective in accelerating inactivation of B[a]P-7,8-diol-9,10-epoxide, the ultimate carcinogenic metabolite that binds to DNA. 相似文献
83.
Structural and catalytic properties of copper in lysyl oxidase 总被引:3,自引:0,他引:3
S N Gacheru P C Trackman M A Shah C Y O'Gara P Spacciapoli F T Greenaway H M Kagan 《The Journal of biological chemistry》1990,265(31):19022-19027
The spectral and catalytic properties of the copper cofactor in highly purified bovine aortic lysyl oxidase have been examined. As isolated, various preparations of purified lysyl oxidase are associated with 5-9 loosely bound copper atoms per molecule of enzyme which are removed by dialysis against EDTA. The enzyme also contains 0.99 +/- 0.10 g atom of tightly bound copper per 32-kDa monomer which is not removed by this treatment. The copper-free apoenzyme, prepared by dialysis of lysyl oxidase against alpha,alpha'-dipyridyl in 6 M urea, catalyzed neither the oxidative turnover of amine substrates nor the anaerobic production of aldehyde at levels stoichiometric with enzyme active site content, thus contrasting with the ping pong metalloenzyme. Moreover, the spectrum of the apoenzyme was not measurably perturbed upon anaerobic incubation with n-butylamine, while difference absorption bands were generated at 250 and 308 nm in the spectrum of the metalloenzyme incubated under the same conditions. A difference absorption band also developed at 300-310 nm upon anaerobic incubation of pyrroloquinoline quinone, the putative carbonyl cofactor of lysyl oxidase, with n-butylamine. Full restoration of catalytic activity occurred upon the reconstitution of the apoenzyme with 1 g atom of copper/32-kDa monomer, whereas identical treatment of the apoenzyme with divalent salts of zinc, cobalt, iron, mercury, magnesium, or cadmium failed to restore catalytic activity. The EPR spectrum of copper in lysyl oxidase is typical of the tetragonally distorted, octahedrally coordinated Cu(II) sites observed in other amine oxidases and indicates coordination by at least three nitrogen ligands. The single copper atom in the lysyl oxidase monomer is thus essential at least for the catalytic and possibly for the structural integrity of this protein. 相似文献
84.
A Meisels M Roy M Fortier C Morin M Casas-Cordero K V Shah H Turgeon 《Acta cytologica》1981,25(1):7-16
We report on 162 cases of human papillomavirus (HPV) infection of the cervix seen in a two-year period in which the cell sample showed such marked atypia that errors of interpretation could easily have been made. These atypical condylomata are difficult to diagnose cytologically as well as histologically because they mimic dysplasia or carcinoma in situ and, on smears, even invasive squamous carcinoma. HPV particles associated with fibrillar material were found within nuclei of these lesions; their nature was further proved by the immunoperoxidase test. This new form of HPV infection of the cervix showed a 9.1% rate of progression to more advanced cervical lesions. The cytologic finding of atypical condylomata is an indication for colposcopy, confirmative biopsy and appropriate treatment. 相似文献
85.
The courses of infection in inbred mouse strains were compared following infection with three Stabilates of high, intermediate, and low virulence of Trypanosoma vivax stock Zaria Y486. Mouse strains could only be shown to differ in their resistance to T. vivax infections as judged by the height of the initial parasitemia and survival times when a trypanosome population of low or intermediate virulence was used. A T. vivax population of high virulence was uniformly lethal. Comparison of lytic antibody titers between groups of resistant () and susceptible () mice did not show any significant differences in titers of the surviving mice but the mice in either group which did not control the initial parasitemia had lower lytic antibody titers than those which did. A significantly larger number of mice failed to control the initial infection as compared to the . Treatment with cyclophosphamide did not ablate differences in susceptibility between the two strains. The use of congenic mice showed that these differences in susceptibility were not related to differences in the major histocompatibility complex between these strains. 相似文献
86.
Nitrate-cultured cells of Phaeodactylum tricornutum Bohlin lack the ability to take up guanine but can do so after a period of nitrogen deprivation, i.e. photosynthesis in nitrogen-free medium. Maximum rate of uptake occurred after 24 h of nitrogen deprivation. The development of ability to take up guanine required CO2 fixation and was prevented by cycloheximide, ammonium or nitrate. The guanine taken up accummulated in the cells almost entirely as a compound which is probably methylated hypoxanthine. Guanine uptake was dependent upon metabolism and exhibited Michaelis-Menten like kinetics with a half-saturation value of 0.48 ± 0.05 μM guanine and a maximum uptake rate for guanine of ca. 200 nmol · 10?8 cells · h?1. Rate of uptake increased hyperbolically with Na+ concentration, with 8.25 mM Na+ supporting half-maximal rate, and it was inhibited by K+ ions. 相似文献
87.
The effects of hyperphenylalaninemia induced by treatment with -methylphenylalanine (MPA) plus phenylalanine (PHE) on body and brain weight, on myelin and synaptosome formation, and on the lipids and fatty acids of myelin were studied in rats. The administration of MPA (2.4 mol/g body wt) plus PHE (2.6 mol/g body wt) for 25 and 35 days beginning on the fifth postnatal day did not affect brain development. On doubling the dosage of PHE, body and brain weights and myelin yields were significantly lowered. The lipid composition of myelin from the brains of treated animals was largely unaffected; however, the concentration of sulfatides was significantly reduced. Unsaturated fatty acid levels in myelin from hyperphenylalaninemic rat brains were reduced while long-chain fatty acids were unaffected. We conclude that as in hyperphenylalaninemia induced by other methods, MPA+PHE treatment impairs body and brain growth, reduces myelin formation, and causes inhibition of fatty acid desaturation in the brain. 相似文献
88.
Pregnant hamsters were treated with different doses of oral and intravenous diazepam during the period of organogenesis. Teratogenic effects of diazepam were observed following oral treatment on days 8 and 10 and following intravenous treatment on day 11 of gestation. Types of malformations included cleft palate, exencephaly, limb anomalies, and hemorrhage. A dose-effect relationship was not observed. Comparison with reported literature seems to indicate that diazepam may be a mild teratogen in some species. 相似文献
89.
Miss Nandita Shah 《Histochemistry and cell biology》1976,46(2):173-175
Summary The histochemical localization of ascorbic acid in plant tissues with the alcoholic acidic silver nitrate reagent is shown
here to be not specific for ascorbic acid, since some of the polyphenolic substances, including flavonoids, which are known
to be widely distributed in plant tissues, are also able to reduce the acidic alcoholic silver nitrate reagent at low temperature
(0–4°C) and at pH 2 to 2.5 in dark. This method may perhaps be used for animal tissues where flavonoid pigments do not occur
in such large quantities as they do in plants. I therefore, come to the inevitable conclusion that the use of alcoholic acidic
silver nitrate reagent in localizing ascorbic acid in plant tissues may be highly misleading. 相似文献
90.
Some kinetic properties of purified component I (Mo-Fe protein) and component II (Fe protein) of nitrogenase (EC 1.7.99.2) from Azotobacter vinelandii have been examined. The apparent Km values for reducible substrates (0.1 atm for N2, 0.01 atm for acetylene) and dithionite (0.5 mM) are similar for osmotically shocked cell lysates and purified components. However, the ATP dependence of acetylene and N2 reduction varies sigmoidally with ATP concentration and as a function of the relative and absolute concentration of components I and II in the assay. Acetylene is reduced in preference to N2 in competitive assays when component I is in relative excess. Acetylene reduction is not as dependent upon ATP concentration as is N2 reduction, so that acetylene is also a preferred substrate at lower ATP levels. Hydrogen specifically inhibits N2 reduction, diverting electrons to acetylene when both substrates are present in the assay. We propose a model of the enzyme activity, in which the substrates for reduction are bound to component I with electrons being activated by component II. ATP may be involved in activating electrons and in maintaining the appropriate conformation or reduction state of components to allow effective reduction of substrates. The relative rate of reduction of alternative substrates is dependent on the concentration of the particular state(s) capable of reacting with each substrate. The concentration of a particular state of component I is a function of components I, II and ATPL 相似文献