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91.
Abstract. The distal inner medullary collecting duct (IMCD) is critical in the urinary concentrating process, in part because it is the site of vasopressin (AVP)-regulated permeability to urea. The purpose of these experiments was to develop a cell culture model of the IMCD on permeable structure and to characterize the responsiveness to AVP. Rat IMCD cells were grown to confluence on collagen-coated Millipore filters glued onto plastic rings. To assess the time required to achieve confluence, the transepithelial resistance was measured periodically and was found to be stable after 2 weeks, at a maximal value of 595 ± 22 ω cm2 . In separate monolayers the effect of AVP on inulin and urea permeability was determined. While inulin permeability was unchanged after AVP, urea permeability increased from 6.0 ± 0–4 to peak values of 16.0 ± 3–8(10nM),23.1 ± 3–9(1 μM)and28 1 ± 4–9(10μM) X 10-6 cms-1 ( n = 24). In 10 other monolayers, after the addition of 1 mM 8-Br-cAMP, urea permeability increased from 5.1 ±0–3 to 8.1 ± 1–6 times 10-6 cm s-1 and, after 8-Br-cAMP +3-isobutyl-l-methylxanthine, to 12.2 ± 0–7 times 10-6 cms-1 . We conclude that rat IMCD cells grown in culture exhibit the characteristics of a 'tight' epithelium. Inulin and urea permeability are not different in the absence of AVP, consistent with high resistance junctional complexes. Furthermore, IMCD cells retain the capacity for AVP-regulated urea permeability, a characteristic feature of this nephron segment in vivo. 相似文献
92.
Hans Georg B?umert Akitsugu Kenmoku Gert Middelhoff Franz Ortanderl Alexander Thrun Heinz Faulstich Wolfgang Schiebler Hugo Fasold 《Journal of Protein Chemistry》1988,7(5):571-580
With the aid of tartryl-bis--aminocaprylazide artificial dimers were produced from F actin from rabbit striated muscle. These derivatives will not polymerize by themselves but are able to copolymerize fully with native G actin. By modification of a single side chain per dimer, this copolymerization was completely inhibited. The dimers are able to activate subfragment I ATPase of myosin and bind to DNase I with inactivation of the enzyme in the same manner as native G actin. Within the dimer, one ADP is immobilized and will exchange against ATP extremely slowly. The dimers do not bind to the mushroom toxin phalloidin. 相似文献
93.
The cyanobacterial photosystem, I complex from Synechococcus sp. PCC6301 contains polypeptides of apparent Mr of 70,000, 18,000, 17,700, 16,000 and 10,000. Procedures were developed for the purification of the Mr 17,700 and 10,000 polypeptides. Amino acid analyses showed the absence of cystine and cysteine from these polypeptides. Amino-terminal sequences of 98 residues for the Mr 17,700 polypeptide and of 42 residues for the Mr 10,000 polypeptide were determined. Studies of pigment distribution within the photosystem I complex indicated that the binding of chlorophyll a and -carotene is in part dependent on the presence of these polypeptides.Abbreviations PSI
photosystem I
- P700
reaction center of PSI
- SDS
sodium dodecylsulfate
- TBS
tris-buffered saline
- TTBS
TBS containing Tween-20 相似文献
94.
95.
96.
Sensitive, high-resolution chromatin and chromosome mapping in situ: presence and orientation of two closely integrated copies of EBV in a lymphoma line 总被引:87,自引:0,他引:87
Here we describe development and application of highly sensitive fluorescence methodology for localization of single-copy sequences in interphase nuclei and metaphase chromosomes by nonisotopic in situ hybridization. Application of this methodology to the investigation of Epstein-Barr virus integration in the Namalwa lymphoma cell line has revealed two EBV genomes closely integrated at the known site on chromosome 1. Detecting sequences as small as 5 kb, we further demonstrate resolution within interphase nuclei of two fragments of the viral genome spaced only 130 kb apart. Results indicate that the viral genomes are in opposite orientations and separated by roughly 340 kb of cellular DNA. This work demonstrates the feasibility and resolving power of interphase chromatin mapping to assess the proximity of closely spaced DNA sequences. Implications for virology, gene mapping, and investigation of nuclear organization are discussed. 相似文献
97.
A study was conducted to determine the role of concentration of the test chemical, of a second organic compound, and of mutation in the acclimation period before the mineralization of organic compounds in sewage. The acclimation period for the mineralization in sewage of 2 micrograms of 4-nitrophenol (PNP) per liter increased from 6 to 12 days in the presence of 10 mg of 2,4-dinitrophenol per liter. The extension of the acclimation period was equivalent to the time required for mineralization of 2,4-dinitrophenol. In contrast, the time for acclimation for the degradation of 2 micrograms of PNP per liter was reduced when 10 or 100 mg of phenol per liter was added. Lower phenol levels increased the acclimation period to 8 days. The length of the acclimation period for PNP mineralization decreased as the initial concentration of PNP increased from 2 micrograms to 100 mg/liter. The acclimation period for phenol mineralization was lengthened as the phenol concentration increased from 100 to 1,400 mg/liter. The length of the acclimation period for PNP and phenol biodegradation was reproducible, but it varied among replicates for the biodegradation of other nitro-substituted compounds added to sewage or lake water, suggesting that a mutation was responsible for acclimation to these other compounds. The acclimation period may thus reflect the time required for the destruction of toxins, and it also may be affected by the concentration of the test compound or the presence of other substrates. 相似文献
98.
Bacterial cell numbers obtained from 103 water and sediment samples from a Pleistocene sandy aquifer in the Lower Rhine region (Bocholt, FRG) were determinated on P-agar and by direct count. Below 5 m under the surface, colony-forming unit (cfu) numbers in water samples were less than 100/ml, and in many cases less than 50/ml. In sediment samples, they were 10- to 100-fold higher (102–104 cfu/g dry wt), but changing markedly between different depths. Direct cell counts yielded numbers two to three orders of magnitude higher.About 2,700 strains of bacteria from 60 samples were isolated randomly and characterized by morphological and physiological properties. Of all the isolates, 71.6% were gram-negative, and 52.2% were gram-negative straight rods. Water communities, with one exception, had low proportions of gram-positive bacteria (<11%), whereas in all but one of the sediment communities percentages of gram-positive isolates were three- to sevenfold higher (35–43%). Water and sediment communities, as well as communities from different sampling sites and communities from different depths of the same sampling site, differed in their qualitative and quantitative morphotype composition and physiological capabilities.The in vitro activities of strains within a single community were quite different, indicating that each community is composed of many diverse bacteria, several having extremely different capabilities. Thus, each community has its own specific activity pattern. Gram-positive bacteria showed on an average lower total activities than did gram-negative bacteria. Grampositive bacteria as well as gram-negative bacteria from sediment had higher values of in vitro activities than the corresponding groups isolated from water. Many water and sediment bacteria preferred the same substrates which were utilized at high rates. However, there were differences in the degradation of the various other substrates present, and each community showed preferences for particular substrates, which they degraded best.The results of cell morphology and physiology studies indicated that all eight characterized communities were very different from one another and very diversely structured. 相似文献
99.
M. A. Alexander V. W. Yang T. W. Jeffries 《Applied microbiology and biotechnology》1988,29(2-3):282-288
Summary
Candida shehatae exhibits different fermentative capacities when grown under different aeration conditions. These studies investigated the titers of xylose reductase, xylitol dehydrogenase, glucose-6-phosphate dehydrogenase and alcohol dehydrogenase in crude extracts ofCandida shehatae grown in continuous culture with various specific aeration rates. Carbon source, aeration rate, dilution rate and temperature were examined as variables. Xylose reductase and xylitol dehydrogenase were induced by xylose and were largely absent in glucose-grown cells. Alcohol dehydrogenae levels were higher in glucose-grown cells than in xylose-grown cells. The levels of this enzyme also correlated with the fermentative character of metabolism, having a low value under fully aerobic conditions, a high value under anaerobic conditions, and intermediate levels under various semi-aerobic conditions. Temperature had no effect on any enzyme level over the range of 20–30°C.Maintained in cooperation with the University of Wisconsin-Madison 相似文献
100.
Vladimir I. Bashkirov Margarita M. Stoilova-Disheva Alexander A. Prozorov 《Molecular & general genetics : MGG》1988,213(2-3):465-470
Summary The illegitimate recombination between Staphylococcus aureus plasmids pE194 (or pGG20, the hybrid between pE194 and Escherichia coli plasmid pBR322) and pBD17 (plasmid pUB110 without HpaII C-fragment) was studied in Bacillus subtilis. Cointegrates were generated with the frequency of 1–3x10-8. Among 22 hybrids analysed 9 types of recombinants were found. Nucleotide sequences of all three parental plasmids were involved in intermolecular recombination. Nucleotide sequencing of recombinant DNA junctions revealed that in 8 cases recombination occurred between short homologous regions (9–15 bp). One recombinant was formed using nonhomologous sites. The similarity was demonstrated between nucleotide sequences of the recombination sites of two types of cointegrates and those used for pE194 integration into the B. subtilis chromosome. Possible mechanisms of illegitimate recombination are discussed. 相似文献