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51.
Peter H. Homann 《Photosynthesis research》1993,38(3):395-400
Under conditions that assured rebinding of the extrinsic 17 and 23 kDa polypeptides, Cl--depleted Photosystem II membranes isolated from spinach chloroplasts were subjected to reconstituting treatments in media containing NaF, NaCl, NaBr, NaI or NaNO3, or they were kept in a medium without any added salt other than the buffer. After removing most of the unbound reconstituting anions by washing, the O2-evolution activities and thermoluminescence properties of the membranes were compared. While the temperature of maximal thermoluminescence emission was lowest for membranes treated with Cl-, no uniform correlation was evident between the temperature profile of the thermoluminescence emission and the apparent activating effectiveness of the anions in the membranes' water oxidizing machinery. However, the differences between the thermoluminescence features did conform to a trend according to which the emission temperatures were upshifted as the size of the activating anion increased, and its hydration energy decreased, i.e. Cl-<Br-<NO3
-<I-. The inactive F- anions were not well retained by the membranes. To explain the experimental data it is suggested that the structural environment of the charge accumulating Mn-center is influenced by the ionic conditions encountered by the Photosystem II membranes after Cl- removal, further enforced by the binding of compatible anions, and then stabilized by the 17 and 23 kDa extrinsic polypeptides. If, as some concepts imply, the anion binding sites are located at or near the functional Mn, only very exceptional characteristics of the water-oxidizing mechanism may account for the observation that the potentially electron-donating I- anion can serve as activator and that it stabilizes rather than destabilizes the S2-state.Abbreviations Chl
chlorophyll
- Hepes
4-(2-hydroxyethyl)-1-piperazine-ethane sulfonic acid
- Mes
2-(N-morpholino)ethane sulfonic acid
- Pheo
the pheophytin a of the Photosystem II reaction center
- PS
photosystem 相似文献
52.
The methyl chloride metabolism of the homoacetogenic, methyl chloride-utilizing strain MC was investigated with cell extracts and cell suspensions of the organism. Cell extracts were found to contain all enzyme activities required for the conversion of methyl chloride or of H2 plus CO2 to acetate. They catalyzed the dechlorination of methyl chloride with tetrahydrofolate as the methyl acceptor at a rate of 20 nmol/min × mg of cell protein. Also, the O-demethylation of vanillate with tetrahydrofolate could be measured at a rate of 40 nmol/min × mg. Different enzyme systems appeared to be responsible for the dehalogenation of CH3Cl and for the O-demethylation of methoxylated aromatic compounds, since cells grown with methoxylated aromatic compounds exhibited a significantly lower activity of CH3Cl conversion than methyl chloride grown cells and vice versa. In addition, ammonium thiocyanate (5 mM) completely inhibited CH3Cl dechlorination, whereas the consumption of vanillate was not affected significantly. The data were taken to indicate, that the methyl chloride dehalogenation is catalyzed by a specific, inducible enzyme present in strain MC, and that tetrahydrofolate rather than the corrinoid-protein involved in acetate formation is the primary acceptor of the methyl group in the dechlorination reaction. 相似文献
53.
Abdullah Jaffer Brian Harvey Vivienne Ann Russell Machteld Elizabeth Carstens Anna Susanna de Villiers Joshua Joachim Fransua Taljaard 《Neurochemical research》1993,18(10):1057-1061
Chronic treatment of rats with lithium chloride was examined in order to determine its effect on hypothalamic monoamine and metabolite content, basal thyrotropin (TSH) secretion and thyroid function. The hypothalamic concentrations of noradrenaline (NA), dopamine (DA) and its metabolites, dihydroxyphenylacetic acid. (DOPAC) and homovanillic acid (HVA) in the lithium treated rats remained unaltered when compared to control levels. NA turnover and the NA metabolite, 3-methoxy-4-hydroxyphenylglycol (total MHPG), were significantly lower (p<0.01), whereas both serotonin (5-HT) and its metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA), were significantly higher (p<0.01 and p<0.02, respectively) in the lithium treated rat hypothalami than in controls. Chronic lithium treatment significantly elevated basal TSH levels (p<0.05). This effect was antagonized by methylp-hydroxybenzoate (methylparaben, p<0.01), which did not itself affect basal TSH levels. Free serum T3 and T4 levels were not significantly affected by chronic lithium treatment, although T4 tended to be slightly lower than control levels. The monoamine changes observed in the hypothalamus of lithium treated rats did not appear to account for the elevated TSH levels observed in these rats since NA activity which is generally regarded as stimulatory was decreased and 5-HT which has an inhibitory effect on TSH secretion, was increased. The elevated TSH levels may have been due to a reduced negative feedback inhibition of TSH release by the mildly reduced circulating T4 levels caused by chronic lithium treatment. A further possibility is that the pituitary cGMP (and hence TSH) response to TRH may have been enhanced by chronic lithium treatment and methylparaben may have antagonized this effect. 相似文献
54.
M. Kondo W. E. Finkbeiner J. H. Widdicombe 《In vitro cellular & developmental biology. Animal》1993,29(1):19-24
Summary Tracheal epithelial cells were grown on Nuclepore filters coated with human placental collagen. When grown immersed in medium
containing fetal bovine serum, cells displayed an undifferentiated ultrastructure (no cilia and a cell height of ∼ 10 μm).
Short-circuit current (Isc) was approximately 1/10 that of the native epithelium. By contrast, when grown in hormonally defined, serum-free medium with
an air interface, cells showed Isc equal to or greater than the original tissue, possessed cilia, and had a cell height of ∼ 50 μm. Responses in Isc to mediators were similar to those of the original tissue, but differed from those of dog or human tracheal epithelium. Given
the ready availability and low cost of the native tissues, bovine tracheal cultures grown in serum-free medium with an air
interface should prove useful in studies of airway epithelial physiology. 相似文献
55.
The osmotic role of nitrate during aftermath growth of Lolium perenne L. cv. Réveille was investigated. Plants were grown from seed in a controlled environment using a liquid medium with 1.0 m M NH4 NO3 as nitrogen source.
Eight-week-old plants were cut 4.0 cm above the root system and then harvested over a 14-day period of regrowth on the same initial nutrient solution, except that nitrate was15 N labelled. Throughout the experimental period, nitrate storage and reduction in roots were low. In stubble and especially in leaves, nitrate accumulated during the first 6 days of regrowth whereas nitrate reduction mainly occurred after this period. Analyses of carbohydrate, chloride and potassium contents in stubble and leaves showed that the accumulation of nitrate osmotically compensated for the decrease in soluble sugars during the first 6 days of regrowth.
The cumulative osmotic potential of sugars, chloride and nitrate in differently treated plants was studied in stubble and leaves. Compared with uncut plants, the lower carbohydrate concentrations found in cut plants regrowing on 1.0 m M NH4 NO3 were compensated for by an accumulation of nitrate. During aftermath growth on low nitrogen nutrition (0.2 m M NH4 NO3 ), chloride replaced nitrate, supporting the proposed osmotic function of nitrate.
It is concluded that nitrate is involved in the osmotic adjustment of ryegrass during regrowth after cutting. 相似文献
Eight-week-old plants were cut 4.0 cm above the root system and then harvested over a 14-day period of regrowth on the same initial nutrient solution, except that nitrate was
The cumulative osmotic potential of sugars, chloride and nitrate in differently treated plants was studied in stubble and leaves. Compared with uncut plants, the lower carbohydrate concentrations found in cut plants regrowing on 1.0 m M NH
It is concluded that nitrate is involved in the osmotic adjustment of ryegrass during regrowth after cutting. 相似文献
56.
Kenneth T. Izutsu Sahba Fatherazi Carol M. Belton Dolphine Oda Frank D. Cartwright George E. Kenny 《In vitro cellular & developmental biology. Animal》1996,32(6):361-365
Summary The relations between K+ channel and Cl− channel currents and mycoplasma infection status were studied longitudinally in HSG cells, a human submandibular gland cell
line. The K+ channel currents were disrupted by the occurrence of mycoplasma infection: muscarinic activation of K+ channels and K+ channel expression as estimated by ionomycin- or hypotonically induced K+ current responses were all decreased. Similar decreases in ionomycin- and hypotonically induced responses were observed for
Cl− channels, but only the latter decrease was statistically significant. Also, Cl− currents could be elicited more frequently than K+ currents (63% of cases versus 0%) in infected cells when tested by exposure to hypotonic media, indicating that mycoplasma
infection affects K+ channels relatively more than Cl− channels. These changes occurred in the originally infected cells, were ameliorated when the infection was cleared with sparfloxacin,
and recurred when the cells were reinfected. Such changes would be expected to result in hyposecretion of salivary fluid if
they occurredin vivo. 相似文献
57.
Soil pH is commonly measured in water (pHw) or 0.01 M CaCl2 (pHCa). The need to convert between these methods has led to the publication of linear, quadratic and cubic polynomial relationships for limited suites of soils. Concerns over the applicability of such relationships when mapping a wide range of soils and pH led to the establishment of a database of pHW and pHCa values on each of 7894 samples from soil survey and field experimental sites in Queensland. The relationship between pHW and pHCa across all soils was investigated and preliminary results examining the effect of soil depth and soil type on the relationship are presented.For all soils and depths, a linear regression accounted for 93.2% of the variation but did not predict pHCa well at very high or low pHW values. The inclusion of second and third powers of pHW accounted for significantly more of the variation (R2=0.94) in pHCa and the resultant curve matched the data better at high and low pH.Analysis of surface, sub-surface and subsoil groupings did not reveal any appreciable differences in the relationship between pHW and pHCa attributable to depth. In contrast, differences in the relationship were evident between soil types. Generally, the mildly leached soils had linear relationships, while the weathered soils were distinctly curvilinear at low pH. 相似文献
58.
Carbamoyl phosphate synthetase I (ammonia; E C 6.3.4.16) was purified from the liver of Rana catesbeiana (bullfrog). Crystals of the protein have been obtained at 22°C by the hanging drop vapor diffusion technique, with polyethylene glycol as precipitant. Tetragonal crystals of about 0.3 × 0.3 × 0.7 mm diffract at room temperature to at least 3.5 Å using a conventional source and are stable to X-radiation for about 12 h. Therefore, these crystals are suitablefor high resolution studies. The space group is P41212 (or its enantiomorph P43212), with unit cell dimensions a = b = 291.6 Å and c = 189.4 Å. Density packing considerations areconsistent with the presence of 4-6 monomers (Mr of the monomer, 160,000) in the asymmetric unit. Amino-terminal sequence of the enzyme and of a chymotryptic fragment of 73.7 kDa containing the COOH-terminus has been obtained. The extensive sequence identity with rat and human carbamoyl phosphate synthetase I indicates the relevance for mammals of structural data obtained with the frog enzyme. © 1995 Wiley-Liss, Inc. 相似文献
59.
Frieder Schauer Kirsten Henning Helmut Pscheidl Rolf M. Wittich Peter Fortnagel Heinz Wilkes Volker Sinnwell Wittko Francke 《Biodegradation》1995,6(2):173-180
Trichosporon beigelii SBUG 752 was able to transform diphenyl ether. By TLC, HPLC, GC, GC-MS, NMR- and UV-spectroscopy, several oxidation products were identified. The primary attack was initiated by a monooxygenation step, resulting in the formation of 4-hydroxydiphenyl ether, 2-hydroxydiphenyl ether and 3-hydroxydiphenyl ether (48:47:5). Further oxidation led to 3,4-dihydroxydiphenyl ether. As a characteristic product resulting from the cleavage of an aromatic ring, the lactone of 2-hydroxy-4-phenoxymuconic acid was identified. The possible mechanism of ring cleavage to yield this metabolite is discussed. 相似文献
60.
Effects of AY 9944 on low density lipoprotein metabolism in cultured human fibroblasts 总被引:1,自引:0,他引:1
J C Mazière C Mazière L Mora J Gardette C Wolf D Rainteau V Barbu C Roux J Polonovski 《Biochemical and biophysical research communications》1984,122(3):955-959
Treatment of cultured human fibroblasts with the hypocholesterolemic drug AY 9944 resulted in a marked increase in low density lipoprotein internalization and degradation for concentrations up to 5 X 10(-6)M. Low density lipoprotein binding was less affected. Concentrations above 5 X 10(-6)M resulted in a relative decrease in low density lipoprotein degradation, whereas binding and internalization plateaued. The stimulation of low density lipoprotein internalization took place within the first hours of incubation of cells with the drug, which suggests a direct effect on the cell membrane. Such phenomenon could account at least partially for the hypocholesterolemic effect of the drug, besides its inhibitory effect on 7-dehydrocholesterol reductase. 相似文献