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  • Articles  (3)
  • Articles: DFG German National Licenses  (3)
  • photoaffinity labeling  (2)
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  • Articles  (3)
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  • Articles: DFG German National Licenses  (3)
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  • 1
    ISSN: 1432-1424
    Keywords: nucleoside transport ; nitrobenzylthioinosine ; p-chloromercuriphenyl sulfonate ; thiol ; red cell ; photoaffinity labeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The sensitivity of nucleoside transport by rat erythrocytes to inhibition by nitrobenzylthioinosine (NBMPR) and the slowly permeating organomercurial,p-chloromercuriphenyl sulfonate (pCMBS), was investigated. The dose response curve for the inhibition of uridine transport (100 μM) by NBMPR was biphasic −35% of the transport activity was inhibited with an IC50 value of 0.25 nM, but 65% of the activity remained insensitive to concentrations as high as 1 μM. These two components of uridine transport are defined as NBMPR-sensitive and NBMPR-insensitive, respectively. Uridine influx by both components was saturable and conformed to simple Michaelis-Menten kinetics, and was inhibited by other nucleosides. The uridine affinity of the NBMPR-sensitive transport component was threefold higher than for the NBMPR-insensitive transport mechanism (apparentK m for uridine 50±18 and 163±28 μM, respectively). The two transport systems also differed in their sensitivity topCMBS. NBMPR-insensitive uridine transport was inhibited bypCMBS with an IC50 of ∼25μM, while 1 mMpCMBS had little effect on NBMPR-sensitive transport by intact cells.pCMBS inhibition was reduced in the presence of uridine and adenosine and reversed by the addition by β-mercaptoethanol, suggesting that thepCMBS-sensitive thiol group is located on the exterior surface of the erythrocyte membrane within the nucleoside binding site of the transport system. Inhibition of uridine transport by NBMPR was associated with high-affinity [3H]NBMPR binding to the cell membrane (apparentK d46±25 pM). Binding of inhibitor to these sites was competitively blocked by uridine and inhibited by adenosine, thymidine, dipyridamole, dilazep and nitrobenzylthioguanosine. Assuming that each NBMPR-sensitive transport site binds a single molecule of NBMPR, the calculated translocation capacity of each site is 25±6 molecules/site per sec at 22°C.pCMBS had no effect on [3H]NBMPR binding to intact cells but markedly inhibited binding to disrupted membranes indicating that the NBMPR-sensitive nucleoside transporter probably has a thiol group located on the inner surface of the membrane. Exposure of rat erythrocyte membranes to UV light in the presence of [3H]NBMPR resulted in covalent radiolabeling of a membrane protein(s) (apparent Mr on SDS gel electropherograms of 62,000). Labeling of this protein was abolished in the presence of nitrobenzylthioguanosine. We conclude that nucleoside transport by rat erythrocytes occurs by two facilitated-diffusion systems which differ in their sensitivity to inhibition by both NBMPR andpCMBS.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    International journal of biometeorology 37 (1993), S. 113-124 
    ISSN: 1432-1254
    Keywords: History ; Climate ; Health ; Tourism ; Hippocratic corpus philosophy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract This paper creates a framework for the study of the history of tourism for climate and health. It traces the ways in which people have both moved away from detrimental health conditions and towards places thought to provide climatic cures. It brings to light the complex issues that have affected the course of the tourist trade. In this way it helps to explain that the modern geographical distribution of the highly fashionable resort areas of the world owe a great deal to past and present interpretations of the HippocraticCorpus.
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  • 3
    ISSN: 1432-1424
    Keywords: nucleoside transport ; adenosine ; nitrobenzylthioinosine (NBMPR) ; microvillous and basal membrane vesicles ; photoaffinity labeling ; human placenta
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The nucleoside transport activity of human placental syncytiotrophoblast brush-border and basal membrane vesicles was compared. Adenosine and uridine were taken up into an osmotically active space. Adenosine was rapidly metabolized to inosine, metabolism was blocked by preincubating vesicles with 2′-deoxycoformycin, and subsequent adenosine uptake studies were performed in the presence of 2′-deoxycoformycin. Adenosine influx by brush-border membrane vesicles was fitted to a two-component system consisting of a saturable system with apparent Michaelis-Menten kinetics (apparentK m approx. 150 μm) and a linear component. Adenosine uptake by the saturable system was blocked by nitrobenzylthioinosine (NBMPR), dilazep, dipyridamole and other nucleosides. Inhibition by NBMPR was associated with high-affinity binding of NBMPR to the brush-border membrane vesicles (apparentK d 0.98±0.21nm). Binding of NBMPR to these sites was blocked by adenosine, inosine, uridine, thymidine, dilazep and dipyridamole, and the respective apparentK i values were 0.23±0.012, 0.36±0.035, 0.78±0.1, 0.70±0.12 (mm), and 0.12 and 4.2±1.4 (nm). In contrast, adenosine influx by basal membrane vesicles was low (less than 10% of the rate observed with brush-border membrane vesicles under similar conditions), and hence no quantitative studies of adenosine uptake could be performed with these vesicles. Nevertheless, high-affinity NBMPR binding sites were demonstrated in basal membrane vesicles with similar properties to those in brushborder membrane vesicles (apparentK d 1.05±0.13nM and apparentK i values for adenosine, inosine, uridine, thymidine, dilazep and dipyridamole of 0.14±0.045, 0.54±0.046, 1.26±0.20, 1.09±0.18mm and 0.14 and 3.7±0.5nm, respectively). Exposure of both membrane vesicles to UV light in the presence of [3H]NBMPR resulted in covalent labeling of a membrane protein(s) with a broad apparentM r on SDS gel electropherograms of 77,000–45,000, similar to that previously reported for many other tissues, including human erythrocytes. We conclude that the maternal (brush-border) and fetal (basal) surface of the human placental syncytiotrophoblast posses broad-specificity, facilitated-diffusion, NBMPR-sensitive nucleoside transporters.
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