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71.
Robin L. Clark 《Hydrobiologia》1986,143(1):63-69
Pollen analysis is widely used to reconstruct vegetation and land use histories, but can also provide sedimentological information. At Burrinjuck Reservoir, in south-eastern Australia, annual grass pollen peaks are used to distinguish each year's sediment, even when there are no visible laminations. In conjunction with other dating methods, this allows the determination of year by year influxes of all sediment components. Pollen grains in the Burrinjuck sediments are shown to be predominantly waterborne so that they can be used to trace sediment to its source in particular vegetation stands. Pollen concentration and the proportion of damaged pollen might also distinguish sediment eroded from topsoils and that from subsoils. Pollen analysis can thus be used to locate specific erosion events in both time and space. 相似文献
72.
Cytologic reports were compared to final diagnoses for 1,157 gastroesophageal samples from an eight-year period in order to evaluate the diagnostic accuracy of endoscopic cytology and to determine the significance of a "suspicious" cytologic report. In the subgroup of patients with adenocarcinoma evaluated by paired endoscopic biopsy and cytology, the relative and combined sensitivities of the sampling methods were studied. Cytologic examination was reported as positive or suspicious in 85% of 229 cases of malignancy. There were three false-positive diagnoses of squamous-cell carcinoma of the esophagus, representing 0.3% of all submitted samples. Suspicious cytologic reports were issued in 5% of all cases. The majority (63%) of patients with a suspicious cytologic report had a final diagnosis of malignancy, with gastric adenocarcinoma present in almost half of the cases. Adenocarcinoma was diagnosed in 168 of the patients. Combined endoscopic biopsy and cytology was more sensitive (96%) than biopsy alone (90%) in making the initial diagnosis. Cytology may be of particular value in the diagnosis of gastroesophageal malignancy when the lesions are small and superficial or where stricture precludes adequate biopsy. Regardless of the biopsy findings, patients with "suspicious" cytologic reports require careful reevaluation since a high percentage of those cases in our series were subsequently verified as having malignancy. 相似文献
73.
Tropomyosin from equine platelets was reacted with N-(1-pyrenyl)iodoacetamide, a sulfhydryl-specific fluorescent reagent, to give an average extent of incorporation of 1.12 pyrene (Py) groups per platelet tropomyosin (P-TM) chain. The predominant site of reaction on P-TM was the penultimate COOH-terminal residue, Cys-246. The high proportion of the total emission that is due to pyrene ecximers and the pretransition observed in thermal denaturation of Py-P-TM point to a rather loose structure for the COOH-terminal amino acid residues of P-TM. The label on Cys-246 also reports on end-to-end overlap interactions that occur between two different tropomyosin molecules. Additions to a Py-P-TM solution at low ionic strength of unlabeled P-TM, rabbit cardiac tropomyosin (C-TM), or a carboxypeptidase A treated, nonpolymerizable derivative of C-TM all reduce the extent of excimer fluorescence from the sample. Addition of salt greatly reduces the effects of the unlabeled TM species on the Py-P-TM emission spectrum. Circular dichroism measurements indicate Py-P-TM still to be greater than 95% helical. However, analysis of excimer fluorescence levels in samples that contained a constant protein concentration but different mole ratios of labeled to unlabeled P-TM suggests that the bulky pyrene group may diminish the tendency of Py-P-TM to polymerize in an end-to-end manner. 相似文献
74.
Effects of several population densities ofMeloidogyne incognita on the sweet potato cultivars Centennial (susceptible) and Jasper (moderately resistant) were studied. Field plots were infested with initial levels (Pi) of 0, 10, 100, 1,000, 5,000, and 10,000 eggs and juveniles/500 cm³ soil in 1980 and 0, 100, 1,000, 2,000, 3,000, 4,000, and 5,000 in 1981. M. incognita population development trends were similar on both cultivars; however, at high Pi, more eggs and juveniles were recovered from Centennial than from Jasper. The highest Pi did not result in the highest mid-season (Pm) counts. Pi was negatively correlated with the number of marketable roots and root weight but positively correlated with total cracked roots, percentage of cracked roots, and cracking severity. Jasper tolerated higher Pi with greater yields and better root quality than Centennial. Cracking of fleshy roots occurred with both cultivars at low Pi. 相似文献
75.
The interactions of Mn2+ and Co2+ with glucose isomerases from three microbial sources have been studied using various direct physical methods. Co2+ was found to activate each enzyme, although the degree of activation varied significantly for enzymes from different organisms. EPR spectroscopy measurements revealed that dissimilarities in the coordination sphere of enzyme-bound Mn2+ accompanied the differences in enzyme activity. Variations in the EPR spectra of a nitroxide spin label coupled to two of the three isomerases, possibly near their active sites, were also observed. In no case was the EPR spectrum influenced by Co2+ addition, a result discordant with the hypothesis that Co2+ activates the enzyme by inducing a conformational change. The proximal biochemical environment of enzymebound Co2+ was also examined using EXAFS spectroscopy. This method showed that glucose causes notable changes in the ligand environment of the enzyme-bound metal, suggesting the formation of an enzyme-metal-substrate bridge complex. The significance of these results relative to possible reaction mechanisms is discussed. 相似文献
76.
77.
We explored the pathologic changes in the skin of mice undergoing a chronic graft-versus-host (GVH) reaction. In rodents and in man, chronic GVH includes the deposition of excess collagen in the skin-a reaction which resembles idiopathic scleroderma. GVH disease across minor histocompatibility barriers was produced by injecting B10.D2 cells into irradiated BALB/c mice. These strains are identical at the H-2 and Mls loci but differ in minor histocompatibility antigens. Control BALB/c mice received irradiation and BALB/c cells. Serial skin biopsies were taken and studied for histological changes characteristic of chronic GVHD, for mast cell density, and for the deposition of immunoreactants. GVHD was produced in B10.D2----BALB/c mice as measured by body weight loss and the production of skin changes including dermal fibrosis, loss of fat and appendages, and a mononuclear cell infiltrate. Dermal mast cells, assessed by toluidine blue staining, were normal at Day 11, but had disappeared by Days 21-63 and returned to normal by Day 104. Immunoglobulins IgG, IgA, and IgM appeared at the dermo-epidermal junction and along the basement membrane zone of hair follicles. This deposition was maximal at Day 42 and waned thereafter. Thus the appearance of immunoglobulins in the skin was maximal when mast cell staining was minimal. The changes in this GVHD model leading to a scleroderma-like picture in the skin are compatible with an immune etiology for the fibrosis. Vasodilation following liberation of mast cell mediators would facilitate the deposition of immunoglobulins. The disappearance of mast cell staining may be caused by extensive degranulation. We postulate an interaction between GVHD-activated T cells, mast cell stimulation, fibroblast activation, and fibrosis. 相似文献
78.
Sedimentation studies of DNA from chromosomes extracted from human mitotic cells showed that highmolecular-weight DNA can be obtained if cell hypotonic treatments and prolonged metaphase blocks are avoided. Two types of large double-stranded DNA were observed. One of these (M
r
= 2.5×108) appeared as a size class with characteristics reminiscent of the chromosomal DNA subunit hypothesis. However, this DNA is the decay product of larger molecules, whose minimum molecular weight is 6×108. 相似文献
79.
Isotope-exchange enhancement studies, a variation on positional isotope-exchange enhancement as described by Raushel and Garrard [Raushel, F. M., & Garrard, L. J. (1984) Biochemistry 23, 1791-1795], are used to establish the point in the biosynthetic reaction of Escherichia coli glutamine synthetase at which gamma-glutamyl phosphate is formed. In these experiments, the behavior of the reverse biosynthetic reaction, i.e., the reaction of ADP, L-glutamine, and phosphate to form NH4+, L-glutamate, and ATP, is examined as a function of the concentration of ammonium ion. By varying the concentration of NH4+, the ratio of the velocity of isotope exchange to the velocity of net reaction, as measured by the rate of 18O depletion from labeled phosphate and the rate of production of L-glutamate, respectively, can be modulated in a mechanism-dependent manner. Evidence is presented demonstrating the presence of a branch point in the mechanism. The enzyme-ATP-glutamate complex may partition in two ways, one involving binding of ammonium ion and the other involving the chemical transformation to form the enzyme-ADP-gamma-glutamyl phosphate complex. The alternate pathways then rejoin upon formation of the enzyme-ADP-NH4+-gamma-glutamyl phosphate complex. Because of the branch point, there is no absolute requirement that ammonium ion be absent or present in order for the formation of gamma-glutamyl phosphate to occur. At high concentrations of ammonia, one pathway through the branch can be eliminated, effectively making that portion of the pathway ordered, with ATP, L-glutamate, and NH4+ binding consistent with our previously reported steady-state kinetic mechanism [Meek, T. D., & Villafranca, J. J. (1980) Biochemistry 19, 5513-5519]. 相似文献
80.
Aluminium salts accelerate peroxidation of membrane lipids stimulated by iron salts 总被引:12,自引:0,他引:12
Aluminium salts do not themselves stimulate peroxidation of ox-brain phospholipid liposomes, but they greatly accelerate the peroxidation induced by iron(II) salts at acidic pH values. This effect of Al(III) is not seen at pH 7.4, perhaps because Al(III) salts form insoluble complexes at this pH in aqueous solution. Peroxidation of liposomes in the presence of Al(III) and Fe(II) salts is inhibited by the chelating agent desferrioxamine, and by EDTA and diethylenetriaminepentaacetic acid at concentrations greater than those of Fe(II) salt. Aluminium salts slightly stimulate the peroxidation of peroxide-depleted linolenic acid micelles, but they do not accelerate the peroxidation induced by addition of iron(II) salts to the micelles at acidic pH. Aluminium salts accelerate the peroxidation observed when human erythrocytes are treated with hydrogen peroxide at pH 7.4. Desferrioxamine decreases the peroxidation. We suggest that Al(III) ions produce an alteration in membrane structure that facilitates lipid peroxidation, and that the increased formation of fluorescent age pigments in the nervous system of patients exposed to toxic amounts of Al(III) may be related to this phenomenon. The ability of desferal to bind both iron (III) and aluminium(III) salts and to inhibit lipid peroxidation makes it an especially useful chelating agent in the treatment of 'aluminium overload'. 相似文献