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71.
Copper is an essential trace element that is utilized in a number of oxygenases and electron transport proteins, but it is also a highly toxic heavy metal, against which all organisms must protect themselves. Known bacterial determinants of copper resistance are plasmid-encoded. The mechanisms which confer resistance must be integrated with the normal metabolism of copper. Different bacteria have adopted diverse strategies for copper resistance, and this review outlines what is known about bacterial copper resistance mechanisms and their genetic regulation. 相似文献
72.
Blood was obtained from 564 11-yr-old children who had participated since birth in a multidisciplinary health and development
study. Serum zinc concentration did not differ between the boys and the girls (mean±SD: 91=17 μg/100 mL,n=453). Five-6% of serum zinc values were low; although there was a weak correlation with height, none of the boys with low
values were below the 10th percentile for height for this group. Serum copper concentration (112±24 μg/100 mL,n=454) was unrelated to sex, height, weight, body mass index, socioeconomic status (SES), or iron status. Blood selenium concentration
(49±10 ng/mL,n=564) was lower than previously reported for Dunedin children; it was higher in children in the lower SES categories. The
data represent normal values for healthy, 11-yr-old NZ children. 相似文献
73.
Flow cytometric analysis and sorting of plant chromosomes from Petunia hybrida protoplasts 总被引:2,自引:0,他引:2
A method to obtain a high metaphase index and thereafter a plant chromosome suspension is described for Petunia hybrida (2n = 14). Mesophyll protoplast cultures have been used, giving easily disrupted cell walls and a high percentage of dividing cells after 42 h. On 2.5 mM colchicine-treated cells, metaphase indexes reaching 10% were routinely obtained. The lysis medium in which the protoplast-derived cells were disrupted was a simplified culture medium. After chromosome release, samples were stained with Hoechst 33342 dye and analysed by flow cytofluorometry. The histogram of fluorescence intensities included three peaks of metaphase chromosomes and a duplication of this flow karyotype provoked by "monochromatid chromosome." This interpretation was established after flow sorting; micronuclei could also be observed and sorted. Of the 7 chromosomes, only the largest formed a distinct peak while the others were incompletely resolved, due to the similar DNA content of various chromosomes. Model distributions of Petunia hybrida chromosomes have been computed according to the relative chromosome length. The theoretical histograms indicated that low variability is indispensable for resolving distinctive chromosome peaks. The experimental flow karyotype was consistent with one of the models having CV of 2.5%. 相似文献
74.
Measurement of plasma adenosine concentration: methodological and physiological considerations 总被引:2,自引:0,他引:2
H Gewirtz P Brown A S Most 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1987,185(1):93-100
This study tested the hypothesis that measurements of plasma adenosine concentration made on samples of blood obtained in dipyridamole and EHNA (i.e., "stopping solution") may be falsely elevated as a result of ongoing in vitro production and accumulation of adenosine during sample processing. Studies were performed with samples of anticoagulated blood obtained from anesthesized domestic swine. Adenosine concentration of ultra filtrated plasma was determined by high-pressure liquid chromatography (HPLC). The following parameters were evaluated: (i) rate of clearance of [3H]adenosine added to plasma, (ii) endogenous adenosine concentration of matched blood samples obtained in "stopping solution" alone, "stopping solution" plus EDTA, and perchloric acid (PCA), (iii) plasma and erythrocyte endogenous adenosine concentration in nonhemolyzed samples, and (iv) plasma adenosine concentration of samples hemolyzed in the presence of "stopping solution" alone or "stopping solution" plus EDTA. We observed that (i) greater than or equal to 95% of [3H]adenosine added to plasma is removed from it by formed elements of the blood in less than 20 s, (ii) plasma adenosine concentration of samples obtained in "stopping solution" alone is generally 10-fold greater than that of matched samples obtained in "stopping solution" plus EDTA, (iii) deliberate mechanical hemolysis of blood samples obtained in "stopping solution" alone resulted in substantial augmentation of plasma adenosine levels in comparison with matched nonhemolyzed specimens--addition of EDTA to "stopping solution" prevented this, and (iv) adenosine content of blood samples obtained in PCA agreed closely with the sum of plasma and erythrocyte adenosine content of samples obtained in "stopping solution" plus EDTA. The data obtained demonstrate that (i) plasma adenosine concentrations are falsely elevated in samples of blood obtained in "stopping solution" alone, and (ii) addition of EDTA to "stopping solution" blocks in vitro production and accumulation of adenosine. Finally, rapid removal of adenosine from plasma by formed elements of blood may make it difficult to employ measurements of plasma adenosine concentration to assess physiological processes even in the absence of in vitro production of the nucleoside. 相似文献
75.
Mammographic changes following reduction mammaplasty 总被引:2,自引:0,他引:2
Mammographic findings after reduction mammaplasty may be similar to those seen with carcinoma. A knowledge of the expected mammographic alterations would be helpful in differentiating postoperative changes from those seen with carcinoma of the breast. Accordingly, the clinical records and mammograms of patients who underwent reduction mammaplasty at the Dartmouth-Hitchcock Medical Center between March of 1977 and July of 1985 were analyzed. Forty-two patients had at least one mammographic examination following reduction mammaplasty. Periareolar soft-tissue changes and inferior pole alterations were present in almost all examinations of patients during the first 6 months after operation, but they decreased during the next few years. Asymmetrical densities were present in approximately half the patients throughout the follow-up period but decreased in degree. Parenchymal calcifications occurred later; few x-rays showed these calcifications during the first year, but 50 percent were apparent after 2 years. Evidence of fat necrosis occurred in approximately 10 percent. Four patients had biopsies for suspicious densities. Chronic inflammation and inclusion cyst were reported. We believe that changes after reduction mammaplasty are predictable and can usually be differentiated from those associated with cancer. 相似文献
76.
Stable monolayers of contact-inhibited C3H 10T1/2 cells were used in multifraction radiation experiments to measure the oxygen enhancement ratio (OER) at low doses/fraction under conditions where cell cycle effects (repopulation, redistribution) were minimal. Consistent with there being a dose-dependent reduction in the OER at low doses, an extremely low OER of 1.34 was measured after 20 fractions of 1.7 Gy every 12 h. The sparing effects of fractionating radiation doses were not apparent for cells irradiated under hypoxic conditions (i.e., multifraction survivals were lower than acute single-dose values) until doses exceeding 15 Gy were reached. This result suggested a deficiency in the recovery from sublethal and/or potentially lethal damage might exist after hypoxic irradiations, thereby reducing the OER. The capacity to repair potentially lethal damage was found to be nearly the same after hypoxic as compared to aerobic irradiations. However, there was an apparent absence of sublethal damage repair by 10T1/2 cells between two hypoxic irradiations which could be a major contributing factor to the extremely low OER value measured in this multifraction schedule. 相似文献
77.
Construction of hybrid Tn501/Tn21 transposases in vivo: identification of a region of transposase conferring specificity of recognition of the 38-bp terminal inverted repeats. 总被引:1,自引:0,他引:1 下载免费PDF全文
In order to study the transposase enzymes of Class II prokaryotic transposable elements, we have constructed genes encoding hybrid transposase proteins. This was done by recombination in vivo between the tnpA genes of transposons Tn501 and Tn21. These hybrid genes can complement in trans a transposition-defective mutant of Tn501. The structures of the products of this complementation indicate whether the specificity of the hybrid transposase in recognising the 38 bp terminal inverted repeats is that of Tn501 or that of Tn21. The determinant of this specificity is in the N-terminal region of the transposase protein, between amino acids 28 and 216. The predicted amino acid sequences so far determined of transposases from the Class II family reveal an area of homology in this region. 相似文献
78.
Proteoglycan metabolism associated with mouse metanephric development: morphologic and biochemical effects of beta-D-xyloside 总被引:3,自引:0,他引:3
Morphology and de novo incorporation of [35S]sulfate into proteoglycans were studied in fetal mouse kidneys at the onset of organogenesis. Branching morphogenesis and nephron development in organ culture and in vivo were associated with de novo synthesis of chondroitin-SO4 and heparan-SO4 proteoglycans. The role of proteoglycan metabolism in metanephrogenesis was then studied by analysis of the effects of p-nitrophenyl-beta-D-xylopyranoside (beta-D-xyloside) on renal development and proteoglycan metabolism. Incubation of fetal kidneys in beta-D-xyloside at concentrations of 1.0 and 0.5 mM, but not at 0.1 mM, caused inhibition of ureteric branching and markedly diminished synthesis of a large Mr 2.0 X 10(6) Da chondroitin-SO4 proteoglycan. Incorporation of [35S]sulfate was stimulated at all beta-D-xyloside concentrations, reflecting synthesis of xyloside initiated dermatan-35SO4 chains. In contrast to dramatic effects on chondroitin-SO4 synthesis and ureteric branching, beta-D-xyloside had no effect on heparan-SO4 synthesis or on development of the glomerulus and glomerular basement membrane. We thus characterize the proteoglycans synthesized early in the course of renal organogenesis and describe observations which suggest an association between metabolism of chondroitin-SO4 proteoglycan and development of the ureter. 相似文献
79.
80.
H D Gresham L T Clement J E Volanakis E J Brown 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(12):4159-4166
Data presented in this paper indicate that polymorphonuclear leukocyte (PMN) Fc receptor-mediated phagocytosis can be markedly augmented and that this augmentation is under regulatory control. Stimulation of PMN with either a low m.w., heat-labile cytokine(s) (the culture supernatant effluent from a YM-10 Centricon unit, YM-10E), phorbol esters (phorbol dibutyrate), or the polyene antibiotic, amphotericin B, enhances Fc-mediated ingestion in a dose-dependent manner. YM-10 effluent- and amphotericin B-stimulated ingestion is completely abrogated by treating the PMN with either pertussis toxin (PT), cholera toxin (CT), or a monoclonal antibody (mAb), 1C2. However, neither toxin nor mAb 1C2 affects nonstimulated ingestion or phagocytosis stimulated by phorbol esters or synthetic diacylglycerol. Increasing intracellular cyclic adenosine monophosphate levels by stimulation with prostaglandin E1 and the phosphodiesterase inhibitor, isobutylmethylxanthine, does not mimic the effect of either toxin or mAb 1C2. In addition, toxin-mediated inhibition is not due to loss of either the Fc receptor recognized by mAb 3G8 or the antigen recognized by mAb 1C2. These data indicate that both CT and PT regulate the phagocytic response of PMN, in a manner like mAb 1C2, probably by affecting a guanosine 5'-triphosphate-binding protein distinct from those that regulate adenylate cyclase. Since phorbol ester-stimulated ingestion is not inhibited by either PT, CT, or mAb 1C2 and phorbol esters activate protein kinase C directly, phagocytosis amplification regulated by PT, CT, and mAb 1C2 may involve protein kinase C activation. 相似文献