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The recBC nuclease (also called exonuclease V) has been partially purified from Escherichia coli K-12 strains carrying the thermosensitive recB270, recC271, and recB270 recC271 mutations. Of the multiple activities associated with the enzyme, only the adenosine 5'-triphosphate-dependent exonucleolytic hydrolysis of duplex deoxyribonucleic acid (DNA) is abnormally thermolabile. The exo- and endonucleolytic degradation of single-stranded DNA is no more thermosensitive than that catalyzed by the wild-type enzyme. These results suggest that the defects in genetic recombination, DNA repair, and the maintenance of cell viability observed in recBC mutants in vivo result primarily from the specific loss of adenosine 5'-triphosphate-dependent exonuclease active on duplex DNA.  相似文献   
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Summary The rate of flow and nitrate and phosphorus content of the water from four drained sandy and clayey plots of size 12×60 m cropped to continuous corn were determined following two annual applications of different rates (0, 260, 390 and 520 kg N/ha) of cow manure slurry. The drain flow was directly related to the rainfall and was greatly influenced by soil texture. The N losses were greater in 1972 (7.8 to 19.1 kg N/ha) than in 1971 (0.4 to 7.8 kg N/ha) because of more summer rainfall. Nitrogen and phosphorus losses were larger from the sandy plots than from the clayey plots. The manure application rates had no apparent effect on nitrogen losses in the drain water.  相似文献   
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Iron is an essential element for diverse biological functions. In mammals, the majority of iron is enclosed within a single prosthetic group: heme. In metazoans, heme is synthesized via a highly conserved and coordinated pathway within the mitochondria. However, iron is acquired from the environment and subsequently assimilated into various cellular pathways, including heme synthesis. Both iron and heme are toxic but essential cofactors. How is iron transported from the extracellular milieu to the mitochondria? How are heme and heme intermediates coordinated with iron transport? Although recent studies have answered some questions, several pieces of this intriguing puzzle remain unsolved.  相似文献   
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The present research was conducted in district Jhang, Pakistan, to evaluate the concentration of metals/metalloids in soil and pumpkin (Cucurbita maxima) irrigated with domestic wastewater. Data revealed that the levels of metals and metalloids in soil samples from two different sites were below the safe limits except Cd, whereas, in the vegetable, the concentrations of As, Se, Ni, Mo, Pb, Mn, and Cu were above the safe limits. The levels of 12 metals and metalloids in the soil were ranged between 0.14 to 22.76 mg/kg at site-I and 0.16 to 22.13 mg/kg at site-II. The levels of these metals in the vegetable were found 0.35 to 61.13 mg/kg at site-I and 0.31 to 53.63 mg/kg at site-II. The transfer factor at both sites was highest for As and Co. The pollution load index recorded for Se, Cu, Cd, Mo, Pb, and Co was greater than 1. The daily intake of As, Mn, and Mo was above the oral reference dose, which reflects that the intake of pumpkin is not safe for the inhabitants of the selected sites. The control measures should be taken to phytoextract heavy metals and metalloids from polluted sites so as to reduce the health risks.  相似文献   
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Sidney Katz 《CMAJ》1987,136(10):1087-1088
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