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Gill T 《Science (New York, N.Y.)》1905,21(542):790-791
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Production of an epidermal growth factor receptor-related protein 总被引:24,自引:0,他引:24
Human epidermoid carcinoma A431 cells in culture produce a soluble 105-kilodalton protein which, by the criteria of epidermal growth factor (EGF) binding, recognition by monoclonal and polyclonal antibodies to the EGF receptor, amino-terminal sequence analysis and carbohydrate content, is related to the cell surface domain of the EGF receptor. The high rate of production and the finding that with biosynthetic labeling the specific activity of this 105-kilodalton protein exceeds that of the intact receptor indicate that it is not derived from membrane-bound mature receptor but is separately produced by the cell. These cells thus separately synthesize an EGF receptor that is inserted into the membrane and an EGF receptor-related protein that is secreted. 相似文献
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Gill HA 《Science (New York, N.Y.)》1917,45(1165):416
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A radiotracer method for the determination of mercury (Hg) methylation rates in bulk water and water overlying intact sediment cores has been developed. A sediment core with overlying water is collected in a core tube, the overlying water is spiked with high specific activity 203-Hg radiotracer, and the core is incubated at ambient temperature. Aliquots of the overlying water are removed, the Hg is extracted from the sample, and the activity in the extract is measured. A 10–25 fold sample preconcentration is achieved using a dithizone-chloroform extraction technique and a sodium nitrite back extraction step to separate inorganic Hg(II) from monomethylmercury (MMHg). The use of this technique, in conjunction with high specific activity 203-Hg, has allowed for spiking concentrations in the overlying water of approximately 1 ng Hg/L. This spiking level is about the same concentration as the ambient water overlying the core, thus not significantly perturbing the system. Our technique is a significant improvement over previous methodologies which used 203-Hg spike additions of 1 μg Hg/L or higher. The technique was used to measure Hg methylation rates at the Experimental Lakes Area (ELA) in Ontario, Canada during August of 1993 and at an extensively studied estuarine site in Gulf Breeze, Florida, USA during September, 1993 and June, 1994. Multiple cores were collected and spiked with a range of 1 to 11,800 ng Hg (as 203-Hg) into the overlying water. MMHg production at the ELA site indicated rates of 0.25 to 3.7 pg/cm2/day (0.08 to 2.5 % methylation/day). Results from Gulf Breeze were significantly higher at 1.5 to 425 pg/cm2/day or 0.06 to 18 % methylation/day. These rates are one to three orders of magnitude greater than previously measured “specific rates” in bulk water samples and sediments. A direct comparison of rates with previous sediment methylation assay techniques is not possible, however, because of the significant differences between our methodology and previous assay protocols. 相似文献
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Enzyme activities and microbial community structure in semiarid agricultural soils 总被引:15,自引:0,他引:15
Acosta-Martínez V. Zobeck T. M. Gill T. E. Kennedy A. C. 《Biology and Fertility of Soils》2003,38(4):216-227
This study investigated the effect of management on -glucosidase, -glucosaminidase, alkaline phosphatase, and arylsulfatase activities and the microbial community structure in semiarid soils from West Texas, USA. Surface samples (0–5 cm) were taken from a fine sandy loam, sandy clay loam, and loam that were under continuous cotton ( Gossypium hirsutum L.) or in cotton rotated with peanut ( Arachis hypogaea L.), sorghum ( Sorghum bicolor L.), rye ( Secale cereale) or wheat ( Triticum aestivum L.), and had different water management (irrigated or dryland), and tillage (conservation or conventional). The enzyme activities were higher in the loam and sandy clay loam than in the fine sandy loam. Soil pH was not affected by management, but the soil organic C and total N contents were generally affected by the different crop rotations and tillage practices studied. The trends of the enzyme activities as affected by management depended on the soil, but in general crop rotations and conservation tillage increased the enzyme activities in comparison to continuous cotton and conventional tillage. The soil enzyme activities were significantly correlated with the soil organic C ( r -values up to 0.90, P< 0.001), and were correlated among each other ( r -values up to 0.90, P <0.001). There were differences in the fatty acid methyl ester profiles between the fine sandy loam and the sandy clay loam and loam, and they reflected the differences in the enzyme activities found among the soils. For example, a 15:0 ranged from 1.61±0.25% in cotton-peanut/irrigated/no-till in the fine sandy loam to 3.86±0.48% in cotton-sorghum/dryland/conservation tillage in the sandy clay loam. There were no differences due to management within the same soil.Trade names and company names are included for the benefit of the reader and do not infer any endorsement or preferential treatment of the product by USDA-ARS 相似文献