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141.
Arginine residues are generally considered poor candidates for the role of general bases because they are predominantly protonated at physiological pH. Nonetheless, Arg residues have recently emerged as general bases in several enzymes: IMP dehydrogenase, pectate/pectin lyases, fumarate reductase, and l-aspartate oxidase. The experimental evidence suggesting this mechanistic function is reviewed. Although these enzymes have several different folds and distinct evolutionary origins, a common structural motif is found where the critical Arg residue is solvent accessible and adjacent to carboxylate groups. The chemistry of the guanidine group suggests unique strategies to lower the pK(a) of Arg. Lastly, the presumption that general bases must be predominantly deprotonated is revisited. 相似文献
142.
Proliferating axillary shoots of the difficult-to-root apple cultivar Jonathan acquired an enhanced ability to form adventitious roots with increasing number of subcultures in vitro. The transition between the difficult-to-root and the easy-to-root condition occurred at the fourth subculture.Endogenous levels of free IAA and ABA in shoot tissues were analysed by gas chromatography/mass spectrometry/single ion monitoring (GC/MS/SIM) using negative ion chemical ionisation. Tissues from the mother plants grown in the glasshouse contained more IAA and ABA than those from tissue-culture material. After establishment in vitro there was no variation in the IAA content throughout the subcultures but a decrease in ABA content was observed after the fourth transfer. The IAA/ABA ratio increased from 0.2 in difficult-to-root shoots from the initial culture up to 0.7 in easy-to-root shoots from the long-term subculture. 相似文献
143.
刈割对紫花苜蓿根系生长影响的初步分析 总被引:25,自引:2,他引:25
研究了不同刈割次数对紫花苜蓿根系发育能力的影响。结果表明:刈割抑制紫花苜蓿主根的纵向(垂直)生长,而促进其横向(直径)生长,并使紫花苜蓿侧根发生总数减少和垂直分布的总体格局向表层集中,随着刈割次数的增加,侧根集中分布在土壤表层的比例也增加;刈割使根系生物量和体积总量减少,并随着刈割次数的增加,这种减少趋势更加明显,同时在土壤中的垂直分布变浅。 相似文献
144.
土壤干旱对元宝枫渗透调节能力的影响 总被引:6,自引:0,他引:6
采用盆栽控水法和P—V技术研究分析了不同土壤干旱(速度、程度)条件对元宝枫渗透调节能力的影响。结果表明,元宝枫具有很强的渗透调节能力.但该能力受土壤干旱的速度和程度影响,在缓慢干旱条件下,元宝枫叶片的ψw、ψ0、π100、RWC^0、ROWC^0均明显降低.其中与渗透调节能力直接相关的(π100可下调0.52MPa,ψ0下调1.51MPa。在快速干旱条件下π100和ψ0分别仅下凋0.20MPa和0.48MPa。△π100值也表明缓慢干旱条件下元宝枫渗透调节能力是快速干旱下的45倍。在缓慢干旱条件下.由轻度到中度干旱时其渗透调节能力显著增强(增加270%);由中度到严重干旱时.增加不明显(增加了24.5%)。从3种有机渗透调节物质含量与△π100值的动态变化可见,可溶性糖含量增加对渗透调节能力的贡献是第一位的.其次是Pro、游离氨基酸。 相似文献
145.
Lars Penke Timothy C. Bates Alan J. Gow Alison Pattie John M. Starr Benedict C. Jones David I. Perrett Ian J. Deary 《Evolution and human behavior》2009,30(6):429-437
It has been proposed that a common cause underlies individual differences in bodily and cognitive decline in old age. No good marker for this common cause has been identified to date. Here, fluctuating asymmetry (FA), an indicator of developmental stability that relates to intelligence differences in young adults, was measured from facial photographs of 216 surviving members of the Lothian Birth Cohort 1921 at age 83 and related to their intelligence at ages 11, 79 and 83 years. FA at age 83 was unrelated to intelligence at ages 11 and 79 and to cognitive change between 11 and 79 years. It was, however, associated with intelligence and information processing efficiency at age 83 and with cognitive change between 79 and 83 years. Significant results were limited to men, a result predicted by sex differences in life history tradeoffs and life expectancy. Results were stronger when directional asymmetries were corrected in facial FA measures. Thus, FA is a candidate marker for the common cause of differential senescence. 相似文献
146.
Monitoring of activated sludge settling ability through image analysis: validation on full-scale wastewater treatment plants 总被引:2,自引:0,他引:2
In recent years, a great deal of attention has been focused on the research of activated sludge processes, where the solid–liquid
separation phase is frequently considered of critical importance, due to the different problems that severely affect the compaction
and the settling of the sludge. Bearing that in mind, in this work, image analysis routines were developed in Matlab environment,
allowing the identification and characterization of microbial aggregates and protruding filaments in eight different wastewater
treatment plants, for a combined period of 2 years. The monitoring of the activated sludge contents allowed for the detection
of bulking events proving that the developed image analysis methodology is adequate for a continuous examination of the morphological
changes in microbial aggregates and subsequent estimation of the sludge volume index. In fact, the obtained results proved
that the developed image analysis methodology is a feasible method for the continuous monitoring of activated sludge systems
and identification of disturbances. 相似文献
147.
148.
149.
Sela D Chen L Martin-Brown S Washburn MP Florens L Conaway JW Conaway RC 《The Journal of biological chemistry》2012,287(27):23035-23045
150.
钾细菌JF88菌株解钾作用及应用研究 总被引:5,自引:0,他引:5
采用比浊法测定JF88菌株的解钾能力,其结果为接菌处理水溶性钾比不接菌增加30.5%,可作为钾细菌肥料的生产菌种,对农业环保具有一定的理论和实践意义。 相似文献