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1.
Abstract In Trichodesmium contortum , nitrogenase was detected in only a limited number (about 10%) of microscopically distinguishable, consecutively arranged cells in central regions of the trichomes. Cells with nitrogenase also contained the photosystem II associated pigment phycoerythrin. These cells were not distinguishable from other cells on a structural basis, but were clearly visible at low magnification microscopy as all in the zone were more compact and shorter than those on either side. The compartmentalisation of nitrogenase into a chain of cells and in a possibly photosynthetic environment represents a previously undescribed phenomenon. The nitrogenase containing cells apparently perform the O2 protective function of heterocysts yet are different in several aspects. 相似文献
2.
Metabolic activation and toxicity of a DDT-metabolite, 3-methylsulphonyl-DDE, in the adrenal zona fasciculata in mice 总被引:4,自引:0,他引:4
Whole-body autoradiography of 14C-labelled 3-methylsulphonyl-DDE (3-MeSO2-DDE) in female C57BL mice revealed a heavy accumulation in the adrenal cortex. Fairly high radioactivity appeared in the nasal mucosa and fat, while the labelling of the liver was intermediate. The adrenal radioactivity remained largely unextracted in tissue-sections treated with organic solvents. In the liver and intestinal contents the radioactivity was partly extracted, whereas in all other tissues almost completely extracted. According to light microscopic autoradiography, the tissue-bound adrenal radioactivity was confined to the zona fasciculata, leaving the other adrenal zones devoid of bound material. Incubation of 3-MeSO2-DDE with adrenal tissue (300 X g supernatant) revealed a dose- and time-dependent covalent binding to protein and formation of water-soluble metabolites. The cytochrome P-450 inhibitors metyrapone and carbon monoxide inhibited both covalent binding and polar metabolite formation. Addition of reduced glutathione decreased binding, while polar metabolite formation was increased. Histopathological examination of adrenals from 3-MeSO2-DDE-treated mice revealed extensive vacuolation and necrosis of the zona fasciculata 1-12 days after single doses down to 25 mg/kg. Degenerative changes were observed at 12.5 mg/kg. In contrast to 3-MeSO2-DDE, 14C-labelled 3,3'-bis(methylsulphonyl)-DDE was not accumulated in the adrenal cortex. 3-MeSO2-DDE is thus a persistent environmental pollutant with a unique ability to produce acute toxicity subsequent to metabolic activation in a mammalian tissue. 相似文献
3.
4.
The lcrB (yscN/U) gene cluster of Yersinia pseudotuberculosis is involved in Yop secretion and shows high homology to the spa gene clusters of Shigella flexneri and Salmonella typhimurium. 总被引:29,自引:12,他引:17 下载免费PDF全文
Virulent bacteria of the genus Yersinia secrete a number of virulence determinants called Yops. These proteins lack typical signal sequences and are not posttranslationally processed. Two gene loci have been identified as being involved in the specific Yop secretion system (G. Cornelis, p. 231-265, In C. E. Hormache, C. W. Penn, and C. J. Smythe, ed., Molecular Biology of Bacterial Infection, 1992; S. C. Straley, G. V. Plano, E. Skrzypek, P. L. Haddix, and K. A. Fields, Mol. Microbiol. 8:1005-1010, 1993). Here, we have shown that the lcrB/virB locus (yscN to yscU) encodes gene products essential for Yop secretion. As in previously described secretion apparatus mutants, expression of the Yop proteins was decreased in the yscN/U mutants. An lcrH yscR double mutant expressed the Yops at an increased level but did not secrete Yops into the culture supernatant. The block in Yop expression of the ysc mutants was also circumvented by overexpression of the activator LcrF in trans. Although the Yops were expressed in elevated amounts, the Yops were still not exported. This analysis showed that the ysc mutants were unable to secrete Yops and that they were also affected in the negative Ca(2+)-regulated loop. The yscN/U genes showed remarkably high homology to the spa genes of Shigella flexneri and Salmonella typhimurium with respect to both individual genes and gene organization. These findings indicate that the genes originated from a common ancestor. 相似文献
5.
R N Bergman 《Federation proceedings》1977,36(2):265-270
The rates of storage and release of carbohydrate by the liver are determined by the plasma concentrations of several blood-borne signals; most important are the concentrations of glucose, and of the hormones insulin and glucagon. To understand the complex control relationships of these three signals as they affect the liver, their individual dynamic influences have been determined experimentally, and the findings have been integrated by means of a computer simulation of the pathways of hepatic glycogen metabolism. The simulation studies have led to specific hypotheses about the biochemical effects of glucose and insulin on the liver. The simulation studies have also led to the conclusion that glucose exerts a rapid moment-to-moment influence on the rate of uptake of glucose by the liver. Insulin, however, by exerting a slower influence on the sensitivity of the liver to glucose, is very effective in "optimizing" the amount of glycogen which the liver stores during food intake. Thus, integrated experimental and simulation studies can lead to a view of a physiological regulating system which does not emerge from either approach used alone.- 相似文献
6.
Ronald Levy Yehudit Bergman Olivera Finn 《In vitro cellular & developmental biology. Plant》1981,17(12):1051-1057
Summary In the present paper, we will summarize studies we have performed on two distinct human lymphocyte cell surface antigens defined
by monoclonal antibodies: Leu-1 and HLA-DR.
Presented in the symposium on The Biology of Hybridomas at the 32nd Annual Meeting of the Tissue Culture Association, Washington,
D.C., June 7–11, 1981.
This work was supported by USPHS-NIH Grants CA-21223, AI-11313, and CA-09302.
This symposium was supported in part by the following organizations: Bethesda Research Laboratories, Cetus Corporation, Hybritech
Incorporated, MAB-Monoclonal Antibodies, Inc., National Capital Area Branch of the Tissue Culture Association, New England
Nuclear Corporation, and Ortho Pharmaceutical Corporation. 相似文献
7.
A "random-hit" matrix model is proposed to account for the dynamic and steady state relationship between occupation of bovine renal medullary membrane receptors by [Lys8]vasopressin (LVP) and neurohypophyseal hormones (NHH) and the associated activation of membrane-bound adenylate cyclase. The model was developed by systematic introduction of specific rules concerning receptor coupling into a general structural model which consists of two square matrices of identical size, one composed of homogeneous R ("receptor") units, the second of homogeneous C ("cyclase") units. R units are either occupied (RO) or unoccupied (RU); C units are either active (CA) or inactive (CI). Hormone molecules are envisioned to "collide" with R units randomly; collision with RU leads to "binding", and occupation is maintained for a characteristic mean occupancy time, TO. In this structure, each R unit has an "interaction field" which consists of the "twin" unit in the "C" matrix, and the 4 nearest neighbor C units surrounding the twin. Occupation of an R unit leads to activation of all CI units in the interaction field of that R; CA units in the interaction field are refractory. Thus binding at a given R may "recruit" a variable number of inactive neighboring C units (5, 4, 3, 2, 1, or 0). The model requires that there be individual coupling delays between the moment of binding at a given R and subsequent activation of CI units (mean coupling delay (Td) approximately 10% To). Activation of C units persists as long as the "parent" R is occupied and is maintained for an additional short time interval (Tp) after RO reverts to RU, corresponding to hormone dissociation from receptor. The model accounts for the following previously demonstrated relations between LVP occupation of receptors and adenylate cyclase activation in bovine renal medullary membranes: 1) the shape of the nonlinear steady state relation between normalized (percentage maximal) receptor occupation (O) and cyclase activation (A), uniformly observed in different membrane preparations: 2) variable hormone concentration-dependent trajectories of approach to the final steady state A:O value (A:Oss) which may be either monophasic or biphasic; 3) the loss of intrinsic adenylate cyclase activity observed in bovine membranes for a series of NHH analogs with progressively diminishing affinity for receptors. The model represents an explicit theory of coupling where a successive series of temporal events are quantitatively related to each other and privide major constraints to any interpretation of the molecular organization of receptors and adenylate cyclase units in membranes. The model excludes a number of mechanistic proposals and suggests a new hypothesis for membrane coupling with features which may be generally applicable to other hormone-sensitive adenylate cyclase systems. 相似文献
8.
A quantitative fluorometric assay for detection and characterization of Fc receptors 总被引:1,自引:0,他引:1
A B Schreiber J Hoebeke Y Bergman J Haimovich A D Strosberg 《Journal of immunology (Baltimore, Md. : 1950)》1978,121(1):19-23
A new quantitative fluorometric binding assay that uses fluoresceinated aggregated IgG is proposed for the study of Fc receptors. The method was compared with a radiolabeling binding assay on three well characterized murine cell lines (38C-13, EL4, and BW). The apparent association constant of the binding and the amount of aggregated IgG bound per cell at saturation were calculated. The fluorometric assay enables the detection of 5 X 10(-10) M bound aggregated IgG. Inhibition studies with monomeric IgG, reduced and alkylated aggregated IgG, and aggregated F(ab')2 fragments of IgG confirmed the specificity of the assay. Staphylococcal protein A inhibited the binding of the aggregated IgG to Fc receptors. 相似文献
9.
10.
Competitive Advantage Provided by Bacterial Motility in the Formation of Nodules by Rhizobium meliloti 总被引:10,自引:4,他引:6 下载免费PDF全文
The effect of motility on the competitive success of Rhizobium meliloti in nodule production was investigated. A motile strain formed more nodules than expected when mixed at various unfavorable ratios with either flagellated or nonflagellated nonmotile derivatives. We conclude that motility confers a selective advantage on rhizobia when competing with nonmotile strains. 相似文献