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Many protein enzymes use general acid-base catalysis as a way to increase reaction rates. The amino acid histidine is optimized for this function because it has a pK(a) (where K(a) is the acid dissociation constant) near physiological pH. The RNA enzyme (ribozyme) from hepatitis delta virus catalyzes self-cleavage of a phosphodiester bond. Reactivity-pH profiles in monovalent or divalent cations, as well as distance to the leaving-group oxygen, implicate cytosine 75 (C75) of the ribozyme as the general acid and ribozyme-bound hydrated metal hydroxide as the general base in the self-cleavage reaction. Moreover, C75 has a pK(a) perturbed to neutrality, making it "histidine-like." Anticooperative interaction is observed between protonated C75 and a metal ion, which serves to modulate the pK(a) of C75. General acid-base catalysis expands the catalytic repertoire of RNA and may provide improved rate acceleration. 相似文献
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Hematogenous metastasis requires the arrest and extravasation of blood-borne tumor cells, possibly involving direct adhesive interactions with vascular endothelium. Cytokine activation of cultured human endothelium increases adhesion of melanoma and carcinoma cell lines. An inducible 110-kD endothelial cell surface glycoprotein, designated INCAM-110, appears to mediate adhesion of melanoma cells. In addition, an inducible endothelial receptor for neutrophils, ELAM-1, supports the adhesion of a human colon carcinoma cell line. Thus, activation of vascular endothelium in vivo that results in increased expression of INCAM-110 and ELAM-1 may promote tumor cell adhesion and affect the incidence and distribution of metastases. 相似文献
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Susan Balaba Tumwebaze Eddie Bevilacqua Russell Briggs Timothy Volk 《Agroforestry Systems》2013,87(4):781-795
Estimates of above-ground biomass are required for better planning, sustainable management and monitoring of changes in carbon stocks in agroforestry systems. The objective of this study was to develop and compare biomass equations for Markhamia lutea, Casuarina equisetifolia, Maesopsis eminii and Grevillea robusta grown in a linear simultaneous agroforestry system in Uganda. These species were established in single rows in the middle of fields in 1995 from four-month old seedlings. A total of 57 trees were sampled for this study, 13 for M. lutea, 12 for C. equisetifolia, 16 for M. eminii and 16 for G. robusta. Biomass values of the various tree components (stem, branches and foliage) as well as the total above-ground biomass were fitted to linear and non-linear allometric models using total height, diameter-at-breast height (DBH), crown width as predictor variables. Although both DBH and height are typically used as independent variables for predicting above-ground biomass, the addition of height in biomass equations did not significantly improve model performance for M. eminii, M. lutea and G. robusta. However, addition of height significantly increased the proportion of variation explained in above-ground biomass for C. equisetifolia, while DBH did not significantly improve the prediction of biomass. The study confirmed the need for developing species-specific biomass equations. 相似文献
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M. Previati I. Bevilacqua D. Canone S. Ferraris R. Haverkamp 《Agricultural Water Management》2010,97(3):449-456
Micro-basins are slope management structures built out of earth and stones on hillslopes around cultivated trees (e.g., olive trees) for the harvesting of rainfall and runoff water, and for the rehabilitation of land degraded by water erosion.In this study, the results of an experimental survey for the comparison of soil water content for both inside and outside the micro-basins are analyzed. Measurements are taken after some rainfall events from January to December 2003 in a hilly region of Central Tunisia. The time domain reflectometry technique is used to measure soil moisture in 15 sets of soil profiles (inside and outside) at three different depths. Four different soils are evaluated, i.e., Cambisols, Kastanozems, Arenosols, and Calcisols.The data analysis shows a significant improvement on the water stock obtained by this type of management. The differences in water storage with respect to soil type, depths, and tillage are evident, but strongly connected to farm management. For optimal management conditions an important increase of average water stock is observed; however, for bad or no farm management the amelioration is zero or is even deteriorating the state of vegetation. 相似文献
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Bevilacqua EM 《Science (New York, N.Y.)》1954,120(3131):1106
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This paper presents the results of five experiments in which animal health risks associated with the consumption of crops irrigated with domestic wastewater were evaluated. Forage maize and Tanner grass were irrigated with treated wastewater and used in goats and calves feeding trials. The irrigated crops presented high levels of surface contamination with E. coli (104–107 25 g?1) and salmonellae (up to 1.6 × 104 25 g?1), but none of the animals showed signs of infection or of disease. Further, the microbiological quality of animal products always complied with the Brazilian and European Union standards for food safety. It is suggested that the WHO guideline values for restricted irrigation (≤104 E. coli 100 ml?1 and ≤1 helminth egg l?1), which were developed to protect the health of agricultural field workers, would be equally protective of the health of both animals fed with wastewater‐irrigated crops and humans consuming products from such animals. 相似文献
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Francesca Romana Massacci Silvia Tofani Claudio Forte Micol Bertocchi Carmela Lovito Serenella Orsini Michele Tentellini Lucia Marchi Gaetan Lemonnier Diana Luise Fany Blanc Adrien Castinel Claudia Bevilacqua Claire Rogel-Gaillard Giovanni Pezzotti Jordi Estellé Paolo Trevisi Chiara Francesca Magistrali 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2020,137(1):60-72
Enterotoxigenic Escherichia coli (ETEC) is the aetiological agent of postweaning diarrhoea (PWD) in piglets. The SNPs located on the Mucine 4 (MUC4) and Fucosyltransferase 1 (FUT1) genes have been associated with the susceptibility to ETEC F4 and ETEC F18, respectively. The interplay between the MUC4 and FUT1 genotypes to ETEC infection and the use of amoxicillin in modifying the intestinal microbiota during a natural infection by multiresistant ETEC strains have never been investigated. The aim of this study was to evaluate the effects of the MUC4 and FUT1 genotypes and the administration of amoxicillin through different routes on the presence of diarrhoea and the faecal microbiota composition in piglets naturally infected with ETEC. Seventy-one piglets were divided into three groups: two groups differing by amoxicillin administration routes—parenteral (P) or oral (O) and a control group without antibiotics (C). Faecal scores, body weight, presence of ETEC F4 and F18 were investigated 4 days after the arrival in the facility (T0), at the end of the amoxicillin administration (T1) and after the withdrawal period (T2). The faecal bacteria composition was assessed by sequencing the 16S rRNA gene. We described that MUC4 and FUT1 genotypes were associated with the presence of ETEC F4 and ETEC F18. The faecal microbiota was influenced by the MUC4 genotypes at T0. We found the oral administration to be associated with the presence of diarrhoea at T1 and T2. Furthermore, the exposure to amoxicillin resulted in significant alterations of the faecal microbiota. Overall, MUC4 and FUT1 were confirmed as genetic markers for the susceptibility to ETEC infections in pigs. Moreover, our data highlight that group amoxicillin treatment may produce adverse outcomes on pig health in course of multiresistant ETEC infection. Therefore, alternative control measures able to maintain a healthy faecal microbiota in weaners are recommended. 相似文献