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991.
Xanthan gum production under several operational conditions has been studied. Temperature, initial nitrogen concentration and oxygen mass transfer rate have been changed and average molecular weight, pyruvilation and acetylation degree of xanthan produced have been measured in order to know the influence of these variables on the synthesised xanthan molecular structure. Also, xanthan gum solution viscosity has been measured, and rheological properties of the solutions have been related to molecular structure and operational conditions. The Casson model has been employed to describe the rheological behaviour. The parameter values of the Casson model, tau(0) and K(c), have been obtained for each polysaccharide synthesised under different operational conditions. Both pyruvilation and acetylation degrees and average molecular weight of xanthan increase with fermentation time at any operating conditions. Xanthan molecules with the highest average molecular weight have been obtained at 25 degrees C. Nevertheless, at this temperature acetate and pyruvate radical concentration are lowest. Nitrogen concentration in broth does not show any clear influence over xanthan average molecular weight, although with high nitrogen source concentration xanthan with low pyruvilation degree is produced. 相似文献
992.
The use of flow cytometry (FCM) to quantitatively analyze intracellular compounds is studied. FCM is a very useful technique for individual cell studies in microbial systems, and gives access to information which cannot be obtained in any other way. Nevertheless, it provides data in arbitrary units, that is, relative data. This analytical technique could be employed for kinetic modeling of microbial systems and even for internal phenomena analysis, but for this purpose, absolute data-that is concentration of intracellular compounds-must be used. In this work, relative flow cytometry data are transformed into absolute data by means of calibrations employing the same fluorochromes with another technique: spectrofluorymetry. Calibrations of DNA, RNA, and protein intracellular concentrations are presented for the bacteria, Xanthomonas campestris. Other analytical methods, based on biochemical determinations, were also employed to quantify intracellular compounds, but the results obtained are very poor compared with those achieved by means of spectrofluorymetry (SFM). Calibration equations and data obtained by both techniques are given. Evolutions of protein and nucleic acids during Xanthomonas campestris growth and xanthan gum production are shown. 相似文献
993.
Relationships between phenolics-conjugated polyamines and sensitivity of sugarcane to smut (Ustilago scitaminea) 总被引:1,自引:0,他引:1
Infection of sugarcane buds (var. Barbados 42231) with teliospores of
Ustilago scitaminea changes the pattern of polyamine
conjugation in several organs of 2-month-old plants. Stalks of infected
plants contain SH-spermidine that does not occur in the healthy organ.
Similar results have been obtained for SH-spermine in the first expanded
leaf and in the stem. The amount of SH-cadaverine in the first expanded
leaf, roots and stem of infected plants is always higher than that found
for healthy plants. Some phenolics are also associated with different
polyamine fractions. So, the amount of
p-hydroxybenzoic acid in both SH and PH fractions of
polyamines extracted from the root increases after infection. Syringic acid
is the main phenol associated with the PH fraction in the first expanded
leaf of infected plants, whereas this phenol is mainly associated with both
SH and PH fractions isolated from the stem and the whip. Infection enhances
conjugation of p-courmaric acid to PH polyamines,
whereas caffeic acid appears in the SH fraction in leaf, root and stem.
However, ferulic acid seems to be the main hydroxycinnamic acid derivative
in the whip. Chlorogenic acid is associated with the SH fraction from the
stem of healthy plants although this changes to free phenolics after
infection.Key words:Saccharum officinarum, Ustilago
sciaminea, phenolics, polyamines.
相似文献
994.
Jaime Fábregas Adolfo Domínguez Digna García Álvarez Teresa Lamela Ana Otero 《Biotechnology letters》1998,20(6):623-626
Haematococcus pluvialis was cultured under N– and Mg+2-deficient conditions with two light intensities: 40 and 230 mol m2 s–1. Highest astaxanthin concentration, 49.5 g·ml–1, was obtained when high light was applied under N-deficient conditions. N-deficiency has a greater effect than high light intensity on astaxanthin synthesis by exerting a stronger blocking effect on cell division. The effect of high light was synergetic with the other stress conditions in stimulating the synthesis of astaxanthin. Mg+2 deficiency also stimulated the synthesis of astaxanthin but produced lower concentrations: 7 and 26 g·ml–1 for low and high light intensities respectively. When both N and Mg+2 were absent from the culture media the concentration of astaxanthin was lower than with N-deficiency alone but higher than with Mg+2-deficiency. © Rapid Science Ltd. 1998 相似文献
995.
Nitrogen availability influences the biochemical composition and photosynthesis of tank-cultivated Ulva rigida (Chlorophyta) 总被引:5,自引:0,他引:5
Juan Luis Gómez Pinchetti Elena del Campo Fernández Paula Moreno Díez Guillermo García Reina 《Journal of applied phycology》1998,10(4):383-389
Physiological and biochemical changes in relation to inorganic nitrogen availability were studied for tank-cultivated Ulva
rigida grown under nitrogen- enriched and nitrogen-depleted seawater. U. rigida was initially cultivated in nitrogen-enriched
seawater (daily concentrations of NH4+ and NO3- + NO2- ranged between 0.5–1.7 and 0.06–0.15 mg L-1, respectively), then transferred
to nitrogen-depleted seawater where photosynthetic capacity decreased to zero after 23 d. At the time (14 d) when photosynthetic
rates were lower than 2.0 μmol O2 g-1 FW min-1 and strong bleaching had occurred, some algae were returned to the initial
nitrogen-enriched seawater to study recovery from N-limited growth. Data on biochemical composition (chlorophylls, ash, caloric
content, fatty acids and dietary fibres) and colouration varied significantly depending on the nitrogen conditions. C:N ratios
correlated significantly with biochemical parameters. Fatty acid (FA) synthesis continued during the N-starvation period;
saturated and mono-unsaturated FA increased to a maximun of 72.2%, while poly-unsaturated fatty acids (PUFA) decreased to
27.7%. During the N-enriched recovery period, the reverse was found. C:N ratios above 10 correlated with carbohydrate synthesis
as shown by the dietary fibre level. Under nitrogen enriched conditions, C:N ratios decreased along with a decrease in fibre
level. Under controlled conditions, nitrogen represents a major influence on the development of intensive tank cultivation
of Ulva rigida, not only by affecting parameters closely related to nitrogen metabolism but also some clearly influenced by
carbon uptake.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
996.
997.
998.
Ana B. P��rez-Oliva Concepci��n Olivares Celia Jim��nez-Cervantes Jos�� C. Garc��a-Borr��n 《The Journal of biological chemistry》2009,284(46):31714-31725
Mahogunin ring finger-1 (MGRN1) is a RING domain-containing ubiquitin ligase mutated in mahoganoid, a mouse mutation causing coat color darkening, congenital heart defects, high embryonic lethality, and spongiform neurodegeneration. The melanocortin hormones regulate pigmentation, cortisol production, food intake, and body weight by signaling through five G protein-coupled receptors positively coupled to the cAMP pathway (MC1R–MC5R). Genetic analysis has shown that mouse Mgrn1 is an accessory protein for melanocortin signaling that may inhibit MC1R and MC4R by unknown mechanisms. These melanocortin receptors (MCRs) regulate pigmentation and body weight, respectively. We show that human melanoma cells express 4 MGRN1 isoforms differing in the C-terminal exon 17 and in usage of exon 12. This exon contains nuclear localization signals. MGRN1 isoforms decreased MC1R and MC4R signaling to cAMP, without effect on β2-adrenergic receptor. Inhibition was independent on receptor plasma membrane expression, ubiquitylation, internalization, or stability and occurred upstream of Gαs binding to/activation of adenylyl cyclase. MGRN1 co-immunoprecipitated with MCRs, suggesting a physical interaction of the proteins. Significantly, overexpression of Gαs abolished the inhibitory effect of MGRN1 and decreased co-immunoprecipitation with MCRs, suggesting competition between MGRN1 and Gαs for binding to MCRs. Although all MGRN1s were located in the cytosol in the absence of MCRs, exon 12-containing isoforms accumulated in the nuclei upon co-expression with the receptors. Therefore, MGRN1 inhibits MCR signaling by a new mechanism involving displacement of Gαs, thus accounting for key features of the mahoganoid phenotype. Moreover, MGRN1 might provide a novel pathway for melanocortin signaling from the cell surface to the nucleus. 相似文献
999.
Pinto RM Vicente JJ Muniz-Pereira LC Noronha D 《Memórias do Instituto Oswaldo Cruz》1999,94(6):751-755
The present paper reports acuarioid nematodes recovered from avian hosts. A new species of the genus Schistorophus Railliet, 1916 is proposed based mainly on findings referring to ptilina, spicules and vagina. Ancyracanthopsis coronata (Molin, 1860) Chabaud & Petter, 1959 is referred again in Brazil since its proposition in 1860, from specimens recovered from a Brazilian bird. A revised key to the species of the genus Schistorophus is also presented. 相似文献
1000.
Luis M. Vázquez de Miguel José A. Serrano Blázquez Fernando J. García Barros Manuel Gómez Guillén 《Carbohydrate research》1984,126(1):81-90
Ethyl 2-amino-4,6-O-benzylidene-2-deoxy-d-gluconate adds to acetylenic esters to give sugar enaminones. The following acetylene derivatives have been employed: methyl propiolate, ethyl phenylpropiolate, and dimethyl acetylenedicarboxylate (6). With compound 6, the reaction leads to a mixture of the expected enaminone and the isomeric oxazolidine derivative. The structures and configurations of the new compounds were studied by spectroscopic and chemical methods. 相似文献