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71.
María-Carmen Rodríguez-Yoldi José-Emilio Mesonero Maríaa-Jesús Rodríguez-Yoldi 《Biological trace element research》1995,50(1):1-11
Zinc is an essential trace element necessary to life. This metal may exert some of its physiological effects by acting directly
on cellular membranes, either by altering permeability or by modulating the activity of membrane-bound enzymes. On the other
hand, calcium is an essential element in a wide variety of cellular activities. The aim of the present work was to study a
possible interaction between zinc and calcium on intestinal transport ofd-galactose in jejunum of rabbit in vitro. In media with Ca2+, when ZnCl2 was present at 0.5 or 1 mM, zinc was found to reduce thed-galactose absorption significantly. In Ca2+-free media, where CaCl2 was omitted and replaced isotonically with choline chloride, the sugar transport was not modified by zinc. Verapamil at 10−6
M (blocking mainly Ca2+ transport) did not modify the inhibitory effect of zinc ond-galactose transport. When 10−6
M of A 23187 (Ca2+-specific ionophore) was added with/without Ca2+ to the media, ZnCl2 produced no change in sugar transport. These results could suggest a possible interaction of calcium and zinc for the same
chemical groups of membrane, which could affect the intestinal absorption of sugars. 相似文献
72.
Del Río G Rodríguez ME Munguía ME López-Munguí A Soberón X 《Biotechnology and bioengineering》1995,48(2):141-148
Increased stability at alkaline pH should be a valuable attribute for the utilization of penicillin acylase in bioreactors employed to convert penicillins into 6-aminopenicillanic acid, a precursor of semisynthetic penicillins. In these systems, base is added for pH control, which results in local alkaline conditions that promote enzyme inactivation. Hydrolysis and synthesis reactions are also pH dependent. Here, we report work in which the gene coding for Escherichia coli penicillin acylase was subjected to oligonucleotide-directed random mutagenesis at regions coding for amino acids predicted to be at the surface of the enzyme. The resulting mutant library, cloned in E. coli, was screened by a filter paper assay of the colonies for the presence of penicillin acylase activity with enhanced stability at alkaline pH. Characterization of one of the selected clones revealed the presence of a mutation, Trp431-Arg, which would presumably alter the surface charge of the protein. In vitro experiments demonstrated a near twofold increase in the half-life of the mutant enzyme when stored at pH 8.5 as compared with the wild-type enzyme, with a comparable specific activity at several pH values. In general, the mutant displayed increased stability toward the basic side in the pH-stability profile. (c) 1995 John Wiley & Sons, Inc. 相似文献
73.
José Moreno Herminia Rodríguez M. Angeles Vargas Joaquín Rivas Miguel G. Guerrero 《Journal of applied phycology》1995,7(1):17-23
Ten strains of filamentous, heterocystous nitrogen-fixing blue-green algae (cyanobacteria) were screened for growth performance
and tolerance to temperature, pH, irradiance and salinity, together with their potential as producers of phycobiliprotein
pigments. Phycobiliproteins typically accounted for about 50% total cell protein, the prevalent type being C-phycocyanin,
followed by alloppycocyanin, with levels of 17 and 11% d.wt, respectively, in some strains of Anabaena and Nostoc. C-phycoerythrin was the major pigment in several Nostoc strains, reaching 10% d.wt. Some strains represent, therefore, excellent sources of one or more phycobiliproteins. All strains
tolerated an irradiance of ca 2000 μmol photon m-2 s-1. Anabaena sp. ATCC 33047 and Nostoc sp. (Albufera) exhibited the widest optimum range of both temperature (30–45 and 25–40 °C) and pH (6.5–9.5 and 6.0–9.0) for
growth, the former also showing significant salt tolerance. In an outdoor open system, productivity of cultures of two phycoerythrin-rich
strains of Nostoc was over 20 g (d.wt) m-2 d-1 during summer. The growth performance of the allophycocyanin-rich Anabaena sp. ATCC 33047 in outdoor semi-continuous culture has been assessed throughout the year. Productivity values under optimized
conditions ranged from 9 (winter) to 24 (summer) g (d.wt) m-2 d-1. 相似文献
74.
The effects of metanephrine and normetanephrine have been compared with those from equiactive doses of the origin compounds, adrenaline and noradrenaline, on the pressor responses in rat, in order to determine whether their effects are owed, at least partially, to a releasing presynaptic action of the catecholamines in normal animals as well as those pretreated with reserpine, guanethidine and 6-OH-dopamine. Their effects have likewise been studied in isolated perfused renal arteries both in normal and reserpinized rats. None of the adrenolytic agent used were able either to reduce the duration of the hypertensive response or to accelerate tachyphylaxis. Identical results were obtained in renal artery preparations. It is thus concluded that the catecholamines stored in presynaptic endings are not involved in the observed phenomena and it is suggested that they might depend on the high doses required to produce effects equiactive to those of the origin substances. 相似文献
75.
In a minimal basal medium with glucose at pH 4.0 and 25 degrees C, a lowering of the magnesium and zinc concentrations or increase in the calcium concentration of the medium favoured the yeast-mycelium transition in Sporothrix schenckii. Addition of zinc (1 and 10 mM) inhibited mycelial development and induced reversion to a yeast-like morphology. EDTA and EGTA also delayed germ tube formation, possibly by their calcium-chelating effects or by altering intracellular concentrations of this or other ions. Ionophore X537A also caused a delay in germ tube formation, possibly by interfering with magnesium metabolism in these cells. 相似文献
76.
Summary The seasonal fluctuation of N, P, K, Ca, Mg, Fe, Mn, Mo, and Co, in leaves, roots and nodules of 40–50 year oldAlnus glutinosa trees growing at four different locations along the banks of the Tormes river, in the province of Salamanca, was studied. Also, the evolution of the soil organic matter under the trees sampled was evaluated. The data obtained for the various nutrient elements in the three plant parts are statistically treated at the significance levels of 99–95 per cent, and some remarks as to the nutritional status of the European alder in respect to the nutrients and its contribution to soil nutrient-cycling are provided. A positive correlation was found between N–P, N–K, N–Mg, and N–Mo, in leaves, and between N–P, N–K, N–Fe, N–Mn, and N–Mo in root nodules. In roots only, no significance at any level was obtained between N and any of the elements analyzed. 相似文献
77.
Immunocytochemistry and ultrastructure of the neuropil located ventral to the rat supraoptic nucleus
C. R. Yulis B. Peruzzo Prof. E. M. Rodríguez M.D. Ph.D. 《Cell and tissue research》1984,236(1):171-180
Summary The neuropil located ventral to the SON was investigated by the use of immunoperoxidase staining for neurophysins, oxytocin and vasopressin, and electron miroscopy. The study was performed in six groups of rats: 1) control; 2) infusion of isotonic saline into the CSF; 3) infusion of hypertonic saline into the CSF; 4) drinking hypertonic saline for 4 days; 5) same as group 4 but injection of colchicine into the CSF on second day of dehydration; 6) salt loading for 3 months. In the control rats the ventral neuropil contained a few immunoreactive processes, the general morphology of which was completely different from that of the neurosecretory axons emerging from the SON at its dorsal aspect. In rats of groups 3 to 6 the ventral processes (VP) became loaded with neurosecretory granules, whereas the perikarya and axons were depleted. Based on their general morphology and reactivity pattern it is suggested that the VP are dendrites. Most of these dendrites were embedded in a glial cushion formed by the processes of a particular type of marginal glia. Some of these dendrites enveloped an arteriole penetrating the optic tract. All VP were rich in synaptic contacts. The possibility that the VP of neurosecretory cells may be functionally related to the subarachnoid CSF and the arteriolar blood flow is discussed.Supported by Grant RS-82-18 from Direccíon de Investigaciones, Universidad Austral de Chile 相似文献
78.
Luis Rodríguez Teresa Ruiz Julio R. Villanueva Rafael Sentandreu 《Current microbiology》1978,1(1):41-44
The intracellular invertase ofSaccharomyces cerevisiae is mainly found in a soluble form (91–95%), while only minor amounts are found bound to the internal (4–8%) and plasma membranes
(less than 1%). In the processes of derepression or repression, inhibition of RNA or protein synthesis, or in the presence
of 2-deoxy-d-glucose, the levels of the membrane-bound and external activities are modified in a way in which their relation is clear,
while the soluble enzyme does not change at all. These results, together with the fact that the membrane-bound and the external
enzymes are glycoproteins, suggest a precursor-product relationship between the enzymic forms. 相似文献
79.
From the aerial part of Teucrium chamaedrys a new neo-clerodane diterpenoid, dihydroteugin, has been isolated, besides the previously known diterpenoids teucrin A and teugin. The structure of dihydroteugin, (12S)-15,16-epoxy-2β,6β-dihydroxy-neo-cleroda-13(16), 14-diene-18,19:20,12-diolide, was established by chemical and spectroscopic means and by partial synthesis from teugin. 相似文献
80.
The binding properties of 25 beta-lactam antibiotics to Bacillus megaterium membranes have been studied. The affinities of the antibiotics for the penicillin-binding proteins (PBPs) are also reported. We found that PBP 4 has the highest affinity for nearly all the antibiotics studied whereas PBP 5 has the lowest affinity. Both PBP 4 and PBP 5 appear to be dispensable for the maintenance of bacterial growth and survival and appear to be DD-carboxypeptidases. Only the beta-lactam cefmetazol bound preferentially to PBP 5 and has been used to study the inhibition of DD-carboxypeptidase. Comparative studies with beta-lactam that simultaneously result in (a) binding to PBPs 1 and 3, (b) inhibition of cell growth and (c) lysis, stressed the importance of PBPs 1 and 3 for cell growth and survival. 相似文献