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111.
Two different Escherichia coli capsular polysaccharide depolymerases each associated with one of the coliphage phi K5 and phi K20 总被引:1,自引:0,他引:1
The Escherichia coli capsular polysaccharides (K antigens) K5 and K20 are known as primary receptors for the coliphage phi K5 and phi K20, respectively. A host range study of the phage revealed that E. coli K5 strains were not only lysed by phi K5 but also by phi K20, and furthermore that the E. coli K95 test strain was attacked by phi K5 in addition to K5 strains. In order to find out whether the phage can degrade the K antigens, the interaction of the phage with isolated polysaccharides was studied. It could be demonstrated that phi K5 was able to depolymerize the K5 and K95 polysaccharides and that phi K20 showed degrading activity towards the antigens K20 and K5. Obviously, each of the phages was associated with two different enzyme systems which enabled them to recognize and depolymerize chemically unrelated polysaccharides. 相似文献
112.
Effects of phenolic acids on ammonia oxidation by terrestrial autotrophic nitrifying microorganisms 总被引:2,自引:0,他引:2
Abstract It has been hypothesized that vegetation in certain ecosystems inhibits nitrification in soil by producing phenolic compounds that inhibit oxidation of ammonia by nitrifying microorganisms. This hypothesis is based largely on a report that very low concentrations (10−6 M–10−8 M) of several phenolic acids (notably ferulic acid) completely inhibited NO2 − production in an aqueous suspension of soil treated with (NH4 )2 SO4 and a nutrient solution suitable for growth of Nitrosomonas and other autotrophic nitrifying microorganisms. To evaluate this hypothesis, we determined the effects of three ohenolic acids (ferulic acid, caffeic acid, and p -coumaric on nitrite production by representatives of three genera of terrestrial autotrophic nitrifying microorganisms ( Nitrosospira, Nitrosomonas , or Nitrosolubos ) grown on a defined medium containing NH4 + . We found that nitrite production by the Nitrososspira was not inhibited by ferulic acid, caffeic acid, or p -coumaric acid at concentrations of 10−6 or 10−5 M and was only slightly inhibited when these acids were at a concentration of 10−4 M. We also found that ferulic acid did not markedly inhibit nitrite production by the three genera of nitrifying microorganisms studied, even when its concentration was as high as 10−3 M. These observations invalidate the hypothesis tested because the phenolic acids studied did not significantly retard ammonia oxidation by autotrophic microorganisms even when their concentration in cultures of these microorganisms greatly exceeded their concentrations in soils. 相似文献
113.
Microcirculatory pathways in normal human spleen, demonstrated by scanning electron microscopy of corrosion casts 总被引:3,自引:0,他引:3
Confusion regarding microcirculatory pathways in normal human spleen has arisen due to extrapolation from pathological material and from other mammalian spleens, not to mention difficulties in tracing intricate three-dimensional routes from the study of thin sections or cut surfaces of tissue. We examined microcirculatory pathways in normal human spleens freshly obtained from organ transplant donors. A modified corrosion casting procedure was used to obtain an open view of vessels and their connections. Our results demonstrate: 1) "arteriolar-capillary bundles" within lymphatic nodules and extensive branching of arterioles in the marginal zone (MZ); 2) the marginal sinus around lymphatic nodules; 3) the peri-marginal cavernous sinus (PMCS) outside the MZ or immediately adjacent to the nodule itself; the PMCS receives flow via ellipsoid sheaths and MZ, or directly from arterial capillaries, and drains into venous sinuses; 4) fast pathways for flow into venous sinuses via ellipsoid sheaths; 5) arterial capillary terminations in the reticular meshwork of the red pulp or MZ ("open" circulation); direct connections to venous sinuses also occur ("closed" circulation), although rarely; and 6) numerous open-ended venous sinuses in the MZ, allowing a large proportion of the splenic inflow to bypass the red cell filtration sites in the reticular meshwork and at venous sinus walls. 相似文献
114.
When calf aortic tissue, preincubated under organ culture conditions in the presence of [35S]sulfate, was submitted to a sequential collagenase and elastase digestion and guanidinium chloride extraction, the bulk of proteoheparan sulfate was obtained in the elastase fraction. Ion-exchange chromatography on DEAE-cellulose of the elastase digest under dissociative conditions yielded a proteoglycan fraction that contained heparan sulfate as the sole glycosaminoglycan. The proteoheparan sulfate fraction was resolved into a high-molecular-mass (P-HS 1) and a low-molecular-mass (P-HS 2) fraction by gel filtration on Sephacryl S-400. P-HS 1 has a Mr of 175,000 and possesses four heparan sulfate side-chains (Mr 32,000) covalently bound to the protein core via a galactose- and xylose-containing polysaccharide-protein binding region. The protein core (Mr 38,000), which was obtained after deglycosylation of PG-HS 1 with trifluormethane sulfonic acid, contained in addition a few N-glycosidically linked oligosaccharide units representing a complex type with terminal neuraminic acid residues. P-HS 2 is a single-chain peptidoheparan sulfate of Mr of 38,000 containing one heparan sulfate chain (Mr 32,000) linked to a polypeptide (Mr 6000). The ratio of specific radioactivities of P-HS 1 and P-HS 2 was 1:0.66. 相似文献
115.
Cytology, DNA and host-symbiont relationships of x-like endosymbionts from Paramecium caudatum are described. The symbionts (Caedibacter caryophila, sp. nov.) live in the macronuclei of their hosts. They confer the killer trait upon their hosts and appear well adapted to their endonucleobiotic way of life. R bodies (proteinaceous ribbons associated with killing) are produced, but differ significantly from any of the four R-body classes previously described. C. caryophila and their R bodies were isolated. DNA was extracted from purified symbionts and used to demonstrate that one P. caudatum line harbors a natural mutant which is deficient in R-body production. Melting studies indicate a GC content of 34.6%. No sequence homology between the C. caryophila DNA and the coding sequence for type 51 R-body production was observed. C. caryophila is parasitic, causing the death of its hosts in starving cultures. 相似文献
116.
Alternate pathways of DNA replication in Escherichia coli 总被引:2,自引:0,他引:2
We have described the pcbA1 mutation which enables E. coli cells to replicate DNA in the absence of a functional dnaE gene product if DNA polymerase I (the polA gene product) is present. The pcbA1 mutation phenotypically suppresses multiple dnaEts and dnaEam alleles. The pcbA1/PolI replication pathway differs from normal in sensitivity to certain DNA-damaging agents such as methylmethane sulfonate (MMS) and a lack of damage-directed mutagenesis. We report here cloning of the pcbA1 gene in a multicopy plasmid. The pcbA1 mutation is detected only in cis; therefore, cloning necessitated gene eviction. The pcbA1 gene lies closely- linked to gyrB. We have demonstrated the physical presence of DNA polymerase I in the replicating holoenzyme complex by immunoblotting using dnaEam strains. We conclude that E. coli has two alternate replisome structures: REP-A, in which DNA polymerase I is the functional synthetic subunit; and REP-E, in which the alpha-subunit, product of the dnaE gene, is functional. To investigate further the role of individual DNA polymerases in replication, we have isolated the polB gene on multicopy plasmids. 相似文献
117.
Developmental competence of domestic cat follicular oocytes after fertilization in vitro 总被引:1,自引:0,他引:1
Empirical evaluation of variables affecting oocyte collection, in vitro fertilization, and embryo transfer resulted in establishing a successful procedure for the artificial production of offspring in the domestic cat. Female cats were treated with pregnant mare's serum gonadotropin (PMSG, 150 IU) followed 72 or 80 h later with 100 or 200 IU human chorionic gonadotropin (hCG). After laparoscopic collection, follicular oocytes were inseminated in vitro with ejaculated, processed spermatozoa, cultured (37 degrees C, 5% CO2), and then examined for evidence of fertilization. Two- to 4-cell stage embryos were transferred to the oviducts of oocyte donors. Oocyte donor cats and naturally mated controls also were subjected to sequential laparoscopic examinations and blood sampling to assess corpora lutea (CL) function. At 24-30 h of culture, fewer (p less than 0.001) degenerate oocytes were observed in cats receiving 100 IU hCG (8.2%) compared to those receiving 200 IU (20.6%), regardless of the PMSG-hCG interval. Overall fertilization (48.1%) and cleavage (45.2%, at 30 h post-insemination) rates were greatest following an 80-h PMSG-hCG interval combined with the 100 IU hCG dose. Five of the 6 cats receiving 6 to 18 embryos became pregnant and produced from 1 to 4 kittens/litter. Gonadotropin-treated females subjected to follicular aspiration produced morphologically normal CL and circulating progesterone patterns that were qualitatively similar (p greater than 0.05) to control cats. These data indicate that domestic cat follicular oocytes are capable of fertilization in vitro, but success is dependent on both the timing and dose of the hCG stimulus. Follicles subjected to aspiration appear capable of forming normal, functional CL and the birth of live young after embryo transfer unequivocally demonstrates, for the first time, the developmental competence of in vitro-fertilized carnivore oocytes. 相似文献
118.
H Schmidt G Ehninger R Dopfer M Blaurock R Naumann H Einsele M Haen K Schüch K Jaschonek D Niethammer 《Blut》1988,57(3):139-142
Between 1982 and 1986 51 patients were treated with ciclosporin a (CSA) to prevent graft versus host disease (GvHD) after bone marrow transplantation (BMT). Major side effects of the drug were tremor, hypertension, hepatotoxicity and nephrotoxicity. Acute GvHD 0 degree to II degree occurred in 80% of our patients, and GvHD III degree and IV degree in 20% despite the use of CSA. Two to four days before the onset of GvHD, CSA serum levels were significantly lower on the average in patients who developed GvHD III degree and IV degree compared to the others. Our data indicate that plasma CSA concentrations higher than 250 ng/ml should be achieved to reduce the severity of GvHD after BMT. 相似文献
119.
Structural changes in membranes of large unilamellar vesicles after binding of sodium cholate 总被引:5,自引:0,他引:5
The interaction of the bile salt cholate with unilamellar vesicles was studied. At low cholate content, equilibrium binding measurements with egg yolk lecithin membranes suggest that cholate binds to the outer vesicle leaflet. At increasing concentrations, further bile salt binding to the membrane is hampered. Before the onset of membrane solubilization, diphenylhexatriene fluorescence anisotropy decreases to a shallow minimum. It then increases to the initial value in the cholate concentration range of membrane solubilization. At still higher cholate concentrations, a drop in fluorescence anisotropy indicates the transformation of mixed disk micelles into spherical micelles. Perturbation of the vesicle membranes at molar ratios of bound cholate/lecithin exceeding 0.15 leads to a transient release of oligosaccharides from intravesicular space. The cholate concentrations required to induce the release depend on the size of the entrapped sugars. Cholesterol stabilizes the membrane, whereas, in spite of enhanced membrane order, sphingomyelin destabilizes the membrane against cholate. Freeze-fracture electron microscopy and phosphorus-31 nuclear magnetic resonance (31P NMR) also reflect a change in membrane structure at maximal cholate binding to the vesicles. In 31P NMR spectra, superimposed on the anisotropic line typically found in phospholipid bilayers, an isotropic peak was found. This signal is most probably due to the formation of smaller vesicles after addition of cholate. The results were discussed with respect to bile salt/membrane interactions in the liver cell. It is concluded that vesicular bile salt transport in the cytoplasm is unlikely and that cholate binding is restricted to the outer leaflet of the canalicular part of the plasma membrane. 相似文献
120.
Nigel L. Brown Tapan K. Misra Joseph N. Winnie Annette Schmidt Michael Seiff Simon Silver 《Molecular & general genetics : MGG》1986,202(1):143-151
Summary The DNA sequences of the mercuric resistance determinants of plasmid R100 and transposon Tn501 distal to the gene (merA) coding for mercuric reductase have been determined. These 1.4 kilobase (kb) regions show 79% identity in their nucleotide sequence and in both sequences two common potential coding sequences have been identified. In R100, the end of the homologous sequence is disrupted by an 11.2 kb segment of DNA which encodes the sulfonamide and streptomycin resistance determinants of Tn21. This insert contains terminal inverted repeat sequences and is flanked by a 5 base pair (bp) direct repeat. The first of the common potential coding sequences is likely to be that of the merD gene. Induction experiments and mercury volatilization studies demonstrate an enhancing but non-essential role for these merA-distal coding sequences in mercury resistance and volatilization. The potential coding sequences have predicted codon usages similar to those found in other Tn501 and R100 mer genes. 相似文献