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101.
102.
The heat inactivation of spores ofBacillus cereus irradiated and non-irradiated with X-rays was investigated with respect to their dipicolinic acid (DPA) content. Spores with a high DPA content (98 μg./mg. dry weight) displayed a biphasic heat inactivation curve. This biphasic character of the curve was preserved for the heat inactivation of previously irradiated spores even if the length of the initial lag of inactivation rate was reduced. Spores with a lower DPA content (24 μg./mg. dry weight) display a single-phase logarithmic order of dying from the beginning of heating. In both types of spores differing in the DPA content a pronounced sensitization of radiation-surviving spores toward subsequent heating was observed. 相似文献
103.
104.
Jaroslav Brčák 《Biologia Plantarum》1965,7(2):93-97
Chenopodium species react on infection with tobacco mosaic virus by the formation of chlorotic or necrotic lesions and later by the abscission of infected leaves. A transition of local infection into the stem has been observed exceptionally inChenopodium quinoa, C. hybridum, andC. rubrum, but no systemic infection of the leaves followed. Systemic infection was demonstrated only inC. polyspermum andC. murale. The recovery of new sprouts was demonstrated in C.murale in the late chronic phase of infection. 相似文献
105.
Tarek Bisat Terry R. Brown Claude J. Migeon Gary D. Berkovitz 《In vitro cellular & developmental biology. Plant》1989,25(9):806-812
Summary Because the measurement of aromatase activity in cultured human genital skin fibroblasts has been proposed as a means of studying
estrogen production in men, we investigated the influence of culture conditions on aromatase activity.
Genital skin fibroblasts were seeded onto culture plates at a density of 1×106 cells/plate and aromatase activity was determined over a 1-mo. period. Enzyme activity rose slowly over the first 14 d but
then rose rapidly to a 10-fold higher plateau by Day 28. The rise in aromatase activity was similar whether activity was normalized
for protein or for DNA content. When cells were seeded at the usual density of 1×106 or at 0.25×106 cells/plate, aromatase activity was consistently lower during the first 2 wk in cells plated at lower density, but thereafter
the levels of enzyme activity in the two groups converged. In cells plated at the lower density, the lower activity observed
in the first 2 wk was associated with a lower V
max
. Preincubation of cells plated at one density with conditoned medium from cells plated at the other density did not change
the relatve levels of activity in the two groups. By contrast, dihydrotestosterone (DHT) receptor binding and 5α-reductase
activity were similar at all time points, despite differences in plating density.
In additional experiments, the culture medium was replaced daily rather than every 3rd d, and aromatase activity was assayed
on Day 7. In cells fed daily, DNA and protein content were twice that of cells fed every 3rd d. By contrast, aromatase activity
declined to 30% of the in the latter group. DHT and dexamethasone receptor binding and 5α-reductase activity were similar
in the two groups.
In summary, factors such as plating density, culture density, and frequency of media replacement dramatically influence aromatase
activity in cultured human genital skin fibroblasts. Therefore, the interpretation of aromatase activity data obtained from
cultured cells in relation to physiologic or pathologic states should be viewed with appropriate caution.
The work was supported in part by grants R01 DK 35339 and R01 DK 00180 from the National Institutes of Health, Bethesda, MD,
and by RR 00035 from CLINFO Systems at the Johns Hopkins University School of Medicine, Baltimore, MD. 相似文献
106.
Neural cell recognition molecule F11: homology with fibronectin type III and immunoglobulin type C domains 总被引:27,自引:0,他引:27
We report here the complete cDNA sequence of F11 130 kd polypeptide, a chick neural cell surface-associated glycoprotein implicated in neurite fasciculation and elongation. The predicted protein sequence of 1010 amino acids includes an amino-terminal signal peptide and a carboxy-terminal hydrophobic stretch, which is compatible with the consensus motif for covalent attachment of glycosyl-phosphatidylinositol. Accordingly, F11 lacks an intracellular domain, which is consistent with evidence obtained from protease protection experiments on isolated microsomes. In addition, the molecule comprises six domains related to the immunoglobulin domain type C and four resembling fibronectin repeat type III. Both types of repeats resemble those present in neural cell adhesion molecules L1 and N-CAM. The possible identity of F11 with the chick neural glycoprotein contactin is discussed. 相似文献
107.
Surface distribution of the mannose 6-phosphate receptors in epithelial Madin-Darby canine kidney cells 总被引:8,自引:0,他引:8
We have analyzed the surface polarity of both the cation-independent (CI-MPR) and the cation-dependent (CD-MPR) mannose 6-phosphate receptors in the epithelial Madin-Darby canine kidney (MDCK) cell line grown on polycarbonate filters. The surface localization was studied by plasma membrane domain-specific surface labeling methods and by confocal microscopy using MPR-specific antibodies. The CI-MPR was shown to be exclusively present on the basolateral cell surface. In contrast, the CD-MPR was expressed neither apically nor basolaterally. However, an intracellular pool of CD-MPR could be detected. In MDCKII-RCAr cells, cell surface CI-MPR was shown to recycle between the basolateral plasma membrane and the trans-Golgi network. After exogalactosylation, cell surface CI-MPR acquired sialic acid residues in a time-dependent manner. Furthermore, the basolateral CI-MPR was shown to be functional. Lysosomal enzymes, bearing the mannose 6-phosphate recognition marker, were taken up from the basolateral medium and endocytosed into the cells. Uptake of lysosomal enzymes from the apical side was insignificant and not MPR mediated. These results extend previous immunoelectron microscopic studies on the intracellular polarity of the CI-MPR (Parton, R. G., Prydz, K., Bomsel, M., Simons, K., and Griffiths, G. (1989) J. Cell Biol. 109, 3259-3272) which showed that the CI-MPR was present in basolateral early endosomes and in late endosomes but absent from apical early endosomes. 相似文献
108.
Philip W. Beesley Toni Paladino Irene Hill Claude Gravel Richard B. Hawkes James W. Gurd 《Journal of neurochemistry》1990,54(2):505-512
Glycoprotein gp50 is a neurone-specific, granule cell-enriched glycoprotein that is also a major component of isolated synaptic membranes. Here, we describe the use of a monoclonal antibody, mab SM gp50, to study the postnatal development of gp50 in the brain of normal and thyroid-deficient rats. Radioimmunoassay, enzyme-linked immunosorbent assay, and Western blotting show that gp50 is not detectable in brain until postnatal day 4 (P4) in both forebrain and cerebellum. In forebrain, the rate of increase of gp50 levels is maximal between P12 and P20. It is somewhat later in cerebellum, where peak levels are attained between P30 and P35. Immunocytochemical studies show little detectable gp50-like immunoreactivity before P16, and the staining is still weak, relative to adult tissue, at P25. The intense staining of the granule cell layer characteristic of adult cerebellum predominantly appears after P25. Development of gp50 is severely retarded in the cerebellum of thyroid-deficient rats, particularly during the second and third postnatal weeks. However, by the fourth postnatal week, gp50 levels in normal and hypothyroid animals are comparable. The results indicate that significant alterations in the pattern of gp50 expression continue to occur at a late stage of cerebellar development. In particular, the increase in immunocytochemical staining of the granule cells after P25 is striking in that by this time most major events associated with cerebellar development are essentially complete. 相似文献
109.
The human cystatin C gene (CST3), mutated in hereditary cystatin C amyloid angiopathy,is located on chromosome 20 总被引:9,自引:4,他引:5
Magnus Abrahamson M. Quamrul Islam Josiane Szpirer Claude Szpirer Göran Levan 《Human genetics》1989,83(3):223-226
Summary Hereditary cystatin C amyloid angiopathy has recently been shown to be caused by a point mutation in the cystatin C gene. To determine the chromosomal localization of the gene, 20 human-rodent somatic cell hybrids and a fulllength cystatin C cDNA probe were used. Southern blot analysis of BamHI digested cell hybrid DNA revealed that the probe recognizes a 10.6 kb human specific fragment and that this fragment cosegregates with human chromosome 20. Therefore, the human cystatin C gene (CST3) was assigned to chromosome 20. 相似文献
110.
Evelyn Jabri David R. Quigley Marjorie Alders Maria Hrmova Cathy S. Taft Patricia Phelps Dr. Claude P. Selitrennikoff 《Current microbiology》1989,19(3):153-161
(1–3)--d-Glucan synthase activity ofNeurospora crassa was localized to the plasma membrane by autoradiography of colloidal gold-labeled plasma membranes. The active site of glucan synthase for substrate hydrolysis was determined to be cytoplasmic facing. However, glucan synthase activity present in intact protoplasts was partially sensitive to Novozym 234 and to glutaraldehyde treatments, suggestive that enzyme activity is transmembrane. Enzyme activity also directed the formation of microfibrils in vitro. Taken together, these and previous results support the following scheme for glucan synthesis: 1. The sequential addition of glucose residues from UDP-glucose to glucan chains occurs on the cytoplasmically facing portion of glucan synthase. 2. As each glucan chain is synthesized, it is extruded to the extracytoplasmic side of the plasma membrane. 3. As each chain is extruded, it forms interchain hydrogen bonds with adjacent chains, resulting in glucan microfibril assembly. 相似文献