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71.
Cytokinesis essentially similar to that of vascular plants occurs in Ulothrix, an unbranched filamentous green alga. Plasmodesmata, similar to those of vascular plants, but different from those of many other algae, are also present. Cell plate formation and plasmodesmata also occur in Stigeoclonium, a branched green alga. 相似文献
72.
An epidemic of infectious hepatitis involving 99 patients and employees of a state mental hospital revealed Australia antigen Au(1) to be absent from the blood of all but one of the subjects when tested at six weeks, three months, nine months and 12 to 18 months after onset of jaundice. The single patient with Au(1) at 12 months had no enzyme abnormality to indicate residual liver disease.If Au(1) is the virus of hepatitis these data would support the concept that persistent or long standing viremia is not a feature of epidemic hepatitis. Moreover, results of this study suggest that the Au(1) test should not be used to establish the absence of a past history of hepatitis in blood donors. These data do not establish the value of the Au(1) test in blood donors with active viremia, but do suggest that of 111 patients with recent hepatitis 1 percent had persistent antigenemia and 4 percent probably had circulating antigen antibody complexes and constituted a potential risk to recipients of their blood. The degree of risk to recipients from transfused blood of post-hepatitis patients without demonstrable Au(1) cannot be assessed. 相似文献
73.
Mercuric ions, as well as organomercuric ions and cadmium ions, can inhibit deoxyribonucleic acid-mediated transformation in Bacillus subtilis 168 without decreasing the viability of the total population. Differences in the inhibition of transformation by mercuric ions are identifiable on a temporal and concentration dependence basis. Sensitivity to low concentrations (9.2 x 10(-8) M) appears early in the uptake of deoxyribonucleic acid before the transformed markers have become insensitive to deoxyribonuclease. Resistance to "low concentrations" of Hg(2+) is kinetically indistinguishable from the requirement for magnesium in the transformation process. This inactivation is not reversed by the mercury-binding compound glutathione. Sensitivity to mercuric ions at a higher concentration (5.52 x 10(-7) M) occurs after the donor deoxyribonucleic acid has become insensitive to deoxyribonuclease. These complex interactions between mercuric ions and the process of transformation are discussed. 相似文献
74.
Biogenesis of mitochondria. Phospholipid synthesis in vitro by yeast mitochondrial and microsomal fractions 总被引:6,自引:0,他引:6
The ability in vitro of yeast mitochondrial and microsomal fractions to synthesize lipid de novo was measured. The major phospholipids synthesized from sn-[2-(3)H]glycerol 3-phosphate by the two microsomal fractions were phosphatidylserine, phosphatidylinositol and phosphatidic acid. The mitochondrial fraction, which had a higher specific activity for total glycerolipid synthesis, synthesized phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine and phosphatidic acid, together with smaller amounts of neutral lipids and diphosphatidylglycerol. Phosphatidylcholine synthesis from both S-adenosyl[Me-(14)C]methionine and CDP-[Me-(14)C]choline appeared to be localized in the microsomal fraction. 相似文献
75.
76.
A coupling constant-dihedral angle correlation for the H? Cα? Cβ? H system of amino acid residues in peptides has been derived from a set of model compounds covering the full range of dihedral angles. The expression obtained, J = 11.0 cos2 θ ?1.4 cos θ + 1.6 sin2θ, is close to those already used in pmr studies of peptide conformation, and provides a firmer foundation for them. A factor limiting the precision of this and other “Karplus relations” is illustrated. 相似文献
77.
An Improved Diluent for Rubella Hemagglutination and Hemagglutination-Inhibition Tests 总被引:3,自引:2,他引:1 下载免费PDF全文
Angela E. Auletta Gary L. Gitnick Carrie E. Whitmire John L. Sever 《Applied microbiology》1968,16(5):691-694
Rubella hemagglutinating (HA) antigen was prepared in BHK-21 tissue as 5% cell suspensions and from unconcentrated and 20× concentrated infected supernatant fluids. In some instances, unconcentrated fluids were treated with Tween 80 and ether; cell suspensions were treated with ether alone. Preparations were tested for HA activity in dextrose-gelatin-Veronal (DGV) buffer solutions; 0.85% NaCl; Sorenson's phosphate-buffered saline, pH 7.2; and a diluent of 0.9% NaCl, 0.1% CaCl2 (anhydrous), and 0.1% MgSO4·7H2O. HA titers were consistently two- to fourfold higher in the saline with added Ca++ and Mg++ than in DGV. Hemagglutination-inhibition titers of paired human sera were the same in either diluent. It is suggested that the interaction between rubella HA antigen and the red cells of young (less than 1-day-old) chicks may be at least partially ion dependent and that titers are enhanced by increased quantities of divalent cations. 相似文献
78.
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
79.
Treatment differences were observed in the in vitro adventitious shoot regeneration response from internodal explants of three genotypes of Populus deltoides cultured on media supplemented with five concentrations each of the cytokinins 6-benzyladenine, 2-isopentyladenine, and zeatin. For each of the three genotypes, the greatest number of shoots were consistently regenerated on media containing the cytokinin zeatin. Tissue necrosis resulted when explants from any of the three genotypes were cultured on media supplemented with 6-benzyladenine. A zeatin concentration by genotype interaction was also observed. Genotypic differences in shoot regeneration were observed for 16 genotypes of Populus deltoides when cultured on medium supplemented with 0.5 mgL–1 zeatin. Six genotypes were highly recalcitrant and failed to regenerate shoots. The percent of explants regenerating was greater than 50% for four genotypes.Abbreviations WNA
modified Woody Plant Media
- BA
N6-benzyladenine
- 2-iP
2-isopentenyladenine
- 2,4-D
2,4-dichlorophenoxyacetic acid
- IBA
indole-3-butyric acid
- MS
Murashige Skoog (1962) medium
- NAA
1-naphthaleneacetic acid
- PAR
photosynthetically active radiation
Journal Series No. 8938, Agricultural Research Division, University of Nebraska 相似文献
80.
Characterization of a Nerve Growth Factor-Stimulated Protein Kinase in PC12 Cells Which Phosphorylates Microtubule-Associated Protein 2 and pp250 总被引:15,自引:5,他引:10
Gary E. Landreth Deanna S. Smith Craig McCabe Cynthia Gittinger 《Journal of neurochemistry》1990,55(2):514-523
Treatment of PC12 cells with nerve growth factor (NGF) resulted in the rapid, but transient, activation of a protein kinase which specifically phosphorylated an endogenous 250-kDa cytoskeletal protein (pp250). We report that the microtubule-associated protein, MAP2, is an alternative substrate for the NGF-activated kinase. NGF treatment maximally activated the kinase within 5 min; however, the activity declined with longer exposure to NGF. The enzyme was localized predominantly in microsomal and soluble fractions and phosphorylated MAP2 on serine and threonine residues. The soluble enzyme was fractionated by DEAE chromatography and gel filtration and had an apparent Mr of 45,000. The enzyme was purified to near homogeneity by chromatofocussing and had a pI of 4.9. Kinetic analysis revealed that NGF treatment caused a sevenfold increase in Vmax for MAP2. The Km with respect to the MAP2 substrate was approximately 50 nM and was not altered by NGF treatment. A novel feature of the NGF-stimulated enzyme was its sharp dependence on Mn2+ concentration. The active enzyme is likely to be phosphorylated, because inclusion of phosphatase inhibitors was required for recovery of optimal activity and the activity was lost on treatment of the enzyme with alkaline phosphatase. Histones, tubulin, casein, bovine serum albumin, and the ribosomal subunit protein S-6 were not phosphorylated by this enzyme. The NGF-stimulated kinase was distinct from A kinase, C kinase, or other NGF-stimulated kinases. The rapid and transient activation of the protein kinase upon NGF treatment suggests that the enzyme may play a role in signal transduction in PC12 cells. 相似文献