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51.
Nitrogen fixation, denitrification, and pleomorphic growth in a highly pigmented Spirillum lipoferum. 总被引:12,自引:3,他引:9 下载免费PDF全文
A strain of Spirillum lipoferum with intense red pigmentation was isolated from the roots of Cynodon dactylon "Coastal." This isolate vigorously reduced acetylene when grown in N-free, Na-malate, semisolid agar, and it was identical to S. lipoferum strain SP7 by standard taxonomic tests. Both S. lipoferum SP7 and the C. dactylon root isolate displayed the unique features of being denitrifiers as well as N2 fixers. The N2-dependent growth curve was biphasic: cells in younger cultures showed the characteristic spiral shape and motility, but those in older cultures developed larger, nonmotile, cystlike forms. Nitrogenase activity seemed associated only with younger spiral forms. The red pigment may be a b- or c-type cytochrome. The strong red color, which this strain develops, could be used as a marker in evaluating soil inoculation experiments. 相似文献
52.
Studies were performed to determine the development of cell-mediated cytotoxic response at tumor site in C57BL/6 mice bearing progressively growing FBL-3 ascites leukemia. The effectors isolated from tumor ascites are found to be highly cytotoxic for leukemic target cells. The levels of cytotoxicity obtained with effectors isolated from tumor site are generally higher than those obtained with immune mice. This cytotoxicity is both specific and nonspecific. The specific cytotoxicity against tumor-associated antigen is mainly mediated by T cells and the nonspecific cytotoxicity against unrelated tumor cells is mediated largely by macrophages. The T-cell-enriched preparation did not give significant natural killer activity. When testing the ability of these effectors to produce in vivo immunity against the challenge of FBL-3, it was found that only T cells could confer the transplantation-type immunity, but the immunity was transient. The macrophage-enriched preparation isolated from tumor ascites failed to give in vivo protection. These findings indicate that in FBL-3 system, mice with progressively growing tumors are able to develop immune response against tumor cells. However, this immunity is probably interfered with by a suppressor factor(s) or suppressor cells which restrict their activity to eliminate the tumor cells effectively. 相似文献
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alpha CD3 induced the generation of activated killer cells from resting T cells. Pretreatment of the splenic responders with PMA, a phorbol ester, depleted protein kinase C and induced unresponsiveness to the generation of alpha CD3-induced activated killer (CD3-AK) cells. Addition of exogenous IL-4 (1 U/ml) restored the cytotoxic response, with the maximal effect achieved with 30 to 100 U/ml. The phenotypes of CD3-AK cells maintained in IL-2 or in IL-4, with or without PMA, were the same: Thy1+ and CD8+. These results were reproduced with purified T cells and purified CD8+ cells, indicating that both the effectors and precursors were CD8+ cells and IL-4 had a selective effect to upregulate the CD8+ cells. Similar results were obtained by using SSP (staurosporine), another PKC inhibitor. At 2 days prior to testing, switching the lymphokine added to 2-week PMA- and IL-2-maintained CD3-AK cells reversed their cytolytic activity: switching from IL-2 to IL-4 restored cytolytic activity, and switching from IL-4 to IL-2 reduced cytolytic activity. The cytolytic activity of these CD3-AK cells correlated with their ability to produce BLT-esterase. In the absence of PMA, CD3-AK cells cultured in either IL-2 or IL-4 were cytolytic and contained high levels of BLT-esterase. In contrast, in the presence of PMA, only the IL-4-maintained CD3-AK cells were cytolytic and produced significant amounts of BLT-esterase. The effect of IL-4 was abrogated by the alpha IL-4 antibody 11B11, which reduced the cytolytic activity of CD3-AK and the ability to produce BLT-esterase. The requirement of IL-2 was less stringent and its major role appeared to be maintaining the cell growth. These findings indicate that IL-4 may participate in the regulation of a PKC-independent pathway for the generation of CD3-AK cells by regulating the production of cytolytic granules. 相似文献
55.
H Moses R B Panek E N Benveniste J P Ting 《Journal of immunology (Baltimore, Md. : 1950)》1992,148(11):3643-3651
The IFN-gamma regulation of the HLA-DRA gene was examined in a primary cell type, the astrocyte. Site-specific mutagenesis of the DRA promoter reveals that three known sequences, S, X, and Y, are required for an optimal IFN-gamma response. Specifically for the X sequence, the X1, but not the X2, site is involved in IFN-gamma regulation of HLA-DRA in the astrocyte. Most interesting, a novel IFN-gamma-enhanced protein (IFNEX) with specificity for the X element has consistently been observed in nuclear extracts made from primary astrocytes. The correlation of the functional importance of X1 in IFN-gamma-regulated DRA expression and the enhancement of IFNEX by IFN-gamma strongly suggests that IFNEX may play a crucial role in IFN-gamma-regulated class II MHC gene expression. 相似文献
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Solvent effect on binding thermodynamics of biopolymers 总被引:2,自引:0,他引:2
The indirect solvent-induced effect on the free energy of binding of biopolymers is examined within the framework of classical statistical mechanics. We focus specifically on the role of the solute-solvent hydrogen bonding. In particular, we have estimated the first order solvent effect on the indirect interaction between two biopolymers. We find that the solvent-induced interactions between two hydrophilic groups through water-bridged hydrogen bonds could significantly enhance the binding free energy. Some preliminary estimates indicate that this effect is significant and perhaps could be crucial in molecular recognition processes. Furthermore, we have calculated, from crystal structure data, the distance distribution between all the oxygens and nitrogens on the surface of some proteins that do not belong to the binding domain. In most cases we found an enhanced peak in the range of 4-5 A, which is where we expect to find strong solvent-induced interactions. 相似文献
58.
Comparison of Proteoglycans Extracted by Saline and Guanidinium Chloride from Cultured Chick Retinas 总被引:2,自引:1,他引:1
Abstract: To compare the loosely associated sulfated proteoglycans with those tightly bound to membranes, retinas from 14-day chick embryos were subjected to progressively disruptive techniques. The most easily removed proteoglycans were isolated from the medium in which the tissue was labeled with [35 S]sulfate. On the average, 25% of the glycosaminoglycans were in the labeling medium, 39% were in proteoglycans extracted from the tissue in the balanced salt solution, 32% were in a 4 m -guanidinium chloride (GuCl) fraction, and 4% remained unextracted. These glycosaminoglycans contained, respectively, 28, 28, 40, and 4% of the incorporated [35 S]sulfate. On the basis of electrophoretic mobility and TLC of chondroitinase digests, the ratio of 35 S in chondroitin sulfate to that in heparan sulfate was 4–7 times higher in the medium and balanced salt extracts than in the GuCl extracts. In both extracts there was more 35 S in chondroitin-6-sulfate than in chondroitin-4-sulfate. Dialysis of the extracts against 0.5 M-NaCl resulted in the precipitation of about 12% of the glycosaminoglycans in the saline extracts and about 40% in GuCl extract. These subfractions, which were relatively enriched in heparan sulfate, were largely soluble in dithiothreitol in 8 m -urea (DTT). Similarities between the proteoglycans in the medium and those extracted by balanced salt solutions suggest that the saline-extracted proteoglycans were for the most part loosely associated with cell surfaces or extracellular matrices, whereas the GuCl-extracted proteoglycans probably were bound to membranes. 相似文献
59.
The amino reagent 2,4,6-trinitrobenzenesulfonate (TNBS) was found to inactivate mitochondrial F1-ATPase through covalent labeling, which was not reversed by dithiothreitol. The observed rate of inactivation was retarded by inorganic phosphate, but enhanced by prior labeling of F1 with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-C1). These observations are consistent with the presence of an essential amino group near the bound inorganic phosphate at the catalytic site of F1. A comparison of the observed protection of F1 from NBD-C1 and 5′-p-fluorosulfonyl-benzoyladenosine (FSBA) respectively by inorganic phosphate and by 2′,3′-O-(2,4,6-trinitrophenyl)adenosine 5′-monophosphate (TNP-AMP) suggests that NBD-C1 labels an essential Tyr residue in the positively charged locus for binding the polyphosphate end of ATP, and that FSBA labels an essential Tyr residue in the more hydrophobic locus for binding the adenosine moiety of ATP at the catalytic site of F1. 相似文献
60.
In vivo immunization of C57BL/6 mice with FBL-3, a syngeneic Friend-virus-induced leukemia, can induce a specific, T-cell-mediated cytotoxic response, as measured by the 125IUdR release assay. In vitro it was difficult to generate an analogous, primary cytotoxic response, using a normal spleen responder population. After modification of the splenic responders by adding normal peritoneal cells, this modified population then had the capacity to mount a primary cytotoxic response in the mixed-lymphocyte-tumor cell culture reaction to FBL-3. We have characterized the effector population as well as the helper (peritoneal) cells which were responsible for elevating the cytolytic response to FBL-3. The results indicate that there are at least two populations of cells which are essential for inducing a primary cell-mediated cytotoxic response. First, the effectors which are directly responsible for mediating the cytotoxic reactions and are derived from radiosensitive T cells and second, a helper cell population which is radioresistant and has the characteristics of macrophages. 相似文献