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51.
52.
Role of external calcium in homeostasis of intracellular pH in the cyanobacterium Anabaena sp. strain PCC7120 exposed to low pH 总被引:1,自引:0,他引:1
The role of external Ca2+ in the homeostasis of intracellular pH (pHi) of Anabaena sp. strain PCC7120 in response to a decrease in the external pH (pHex) has been studied in cell suspensions. Increase in cytoplasmic pH after acid shock is dependent on the presence of Ca2+ in the medium. The observed Ca2+ -mediated alkalization of the cytoplasm depends on the extent of the shift in external pH. Acid pH shifts resulted in an increased permeability of the cytoplasmic membrane to protons, which could be reversed by increasing the concentration of Ca2+ in the medium. Thus, the ability of Ca2+ to increase cytoplasmic pH might be correlated with an inhibition of net proton uptake by increasing concentrations of external Ca2+ under these conditions. This combined response resulted in the generation and maintenance of a larger pH gradient (ΔpH) at acid external pH values. All Ca2+ channel blockers tested, such as verapamil and LaCl3 , inhibited the observed Ca2+ -mediated response. On the other hand, the Ca ionophore calcimycin (compound A23187) was agonistic, and stimulated both cytoplasmic alkalization and inhibition of net proton uptake. The protonophorous uncoupler carbonylcyanide m -chlorophenyl hydrazone, inhibited this Ca2+ -mediated response, whereas monensin, an inhibitor of the Na+ /H+ antiporter, had no significant effect. The results of the present study suggest that an influx of Ca2+ from the extracellular space is required for the regulation of cytoplasmic pH in Anabaena sp. strain PCC7120 exposed to low external pH values. 相似文献
53.
Mire Convery Caitríona Dennis Sin Rowsell Andreas Engel J Bernard Heymann Gary Parkinson Rob Russell Gianfranco Gilardi Richard Newman Irmgard Sinning Sabine Flitsch Philip AS Lowden Steve Matthews Gerard J Kleywegt Jon D Stewart 《Current opinion in structural biology》1999,9(6):653
A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in structural biology. 相似文献
54.
Microbial population dynamics on Golden Delicious apples from bud to harvest and effect of fungicide applications 总被引:3,自引:0,他引:3
The microbial population dynamics on apples cv. Golden Delicious were analysed every 15 days between bud and harvest in a fully replicated experiment in northern Spain in 1994 and 1995. The total microbial populations varied with developmental stage, and with prevailing climatic conditions. The predominant mycroflora were the filamentous fungi Cladosporium and Alternaria spp. and white and pink yeasts. Other genera isolated included mainly species of Epicoccum, Fusarium and Acremonium. However, the most important post-harvest pathogens Penicillium expansum and Botrytis cinerea were seldom isolated from ripening apples. Maximum total filamentous fungal populations occurred after fruit set and during early ripening [2 × 104cfu (colony-forming units) g-1 approximately] while those of bacteria were maximum at bud stage (3.5 × 105and 3.0 × 104 cfu g-1 in 1994 and 1995 respectively). White yeasts were more numerous than pink yeasts. Endophytic infection of apple buds by Alternaria spp., responsible for core rot, was found in almost all bud tissue. By contrast, Cladosporium spp. were initially isolated later from 12.5–50% of tissue samples during blooming and fruit set. The impact of a four-spray fungicide regime during apple development significantly decreased the total filamentous fungal populations in both years, and that of Cladosporium spp. in 1994. However, bacterial populations were often higher on apples from fungicide-treated plots. Fungicide sprays decreased populations of Cladosporium, Alternaria and white yeasts for a maximum of up to 15–30 days after application. Fungicide application had little effect on endophytic infection of apples by Alternaria spp. between bud and harvest. 相似文献
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A study was made of the effect of cycloheximide on the radioresistant DNA synthesis stimulated by preincubation of cells with 5-fluorodeoxyuridine (FdUrd). It was shown that after the cycloheximide treatment the radioresistant DNA synthesis was absent while in FdUrd-treated cells it did occur. It is assumed that the FdUrd-stimulated radioresistant DNA synthesis is of an inducible nature. 相似文献
57.
Enzyme immunoassay for ceruloplasmin (CP)*, employing monospecific CP antibodies labeled with horse radish peroxidase was developed. This method permits to determine total content of CP, which is present in Wilson disease patients' blood in enzymatically active and enzymatically inactive forms. The evidence is presented that the method can be used for a direct determination of CP in blood serum. The minimal CP concentration which may be determined by enzyme immunoassay (IEA) is 5.10(-9) g/ml. The method was used for determination of CP concentrations in Wilson disease patients' blood with different disease severity. Analysis of blood samples taken from 6 Wilson disease patients with the use of IEA method revealed similar total CP concentrations. At the same time, the oxidase activities of CP in the blood of different patients varied more than sevenfold. 相似文献
58.
The comparison of protective effects of native ceruloplasmin (CP) and of preparation CP1 containing carbohydrate fragment GlcNAc(beta(1,4]GlcNAc which specifically binds on RBC (alpha(1,6)Fuc receptors showed that CP1 exhibits much more powerful protective effect on RBC in copper-induced lysis. It was found, however, that CP2 (native CP devoided of CP1) protected RBC as well as CP despite its inability of binding to RBC membrane. CP and CP1 in a similar way decrease copper concentration in RBC. It was shown that copper accumulation and GSH decrease in RBC are two independent and concurrent processes; the copper and GSH concentrations are not the factors determining RBC resistance to hemolysis. CP inhibits the reaction of superoxide radicals generation as a result of Cu interaction with -SH groups of RBC membrane; the effect is more pronounced than the effect of catalase or superoxide dismutase. CP and CP1 preparations equally inhibit this reaction. Apparently CP reception on RBC leads not only to membrane protection from superoxide and hydroxyl radicals but represents a more complex process. 相似文献
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