pH titration studies of 13C reductively methylated N-terminal serine of glycophorin AM

The ¹³C resonances of N^α,N-[¹³C]dimethylserine of partially ¹³C reductively methylated glycophorin A^M were monitored as a function of pH at 45°C. For comparison, limited data are also presented for the pH dependence of the ¹³C resonances of N^α,N- [¹³C]dimethylserine of fully ¹³C reductively methylated deglycosylated glycophorin A^M. The ‘major’ component of N^α,N- [¹³C]dimethylserine of glycophorin A^M did not titrate, whereas the ‘minor’ component titrated with a pK_a of 7.80 (Hill coefficient of 0.95). Similar results are also indicated for the N^α,N- [¹³C]dimethylserine resonances of ¹³C reductively methylated deglycosylated glycophorin A^M.     

Involvement of lysine residues in the binding of ovine chorionic somatomammotropin to lactogenic and somatotropic receptors

The biological activities of several ovine chorionic somatomammotropin (oCS) derivatives obtained by chemical modification of the lysine residues were studied by radioreceptor assays using rabbit mammary homogenates (lactogenic activity, L.A.) and liver homogenates (somatotropic activity, S.A.). Even if the control treatment with BH-4 markedly decreased the L.A., it was clear that methylation mainly affected the S.A. and that ethylation reduced both activities. Guanidination inactivated almost completely both activities and acetimidination at a very low degree (3 of 14 lysines) led to less than 50% of both activities. These results show the involvement of lysine residues in the interaction of oCS with lactogenic and somatotropic receptors.     

Renal sodium-d-glucose cotransport system. Involvement of tyrosine residues in sodium-transporter interaction

Using brush-border membrane vesicles isolated from calf kidney cortex the effect of tyrosine-reactive reagents on sodium-dependent d-glucose transport was investigated. Treatment of the membranes for 60 min with NBD-Cl (7-chloro-4-nitrobenzo-2-oxa-1,3-diazole), N-acetylimidazole or tetranitromethane decreased d-glucose uptake 50, 70 and 40%, respectively. Tracer exchange experiments revealed that the inhibition of transport is due to a direct modification of the sodium-d-glucose cotransport system. The modification by NBD-Cl decreases the apparent V_max of the transport system with respect to its interaction with sodium. In addition, the rate of inactivation of the transport system by NBD-Cl is reduced in the presence of high concentrations of sodium. The results indicate that tyrosine residues play an essential role in sodium-d-glucose cotransport and are probably involved in the binding and/or transport of sodium by the sodium-d-glucose cotransport system.     

农药的轭合与结合态残留

随着科技水平的不断提高,人们对农药残留影响生态环境的认识不断在更新和完善。农药的轭合与结合残留是在标记农药的出现和高精度分析仪器和技术得到应用后被发现和认识的。国外在这方面的研究开展得较早,工作也较     

拟除虫菊酯类农药对茶树害虫的生物活性与残留降解

本文报道了溴氰菊酯、联苯菊酯、氯氰菊酯、顺式氯氰菊酯、杀灭菊酯、功夫菊酯和二氯苯醚菊酯等七种拟除虫菊酯类农药对茶树主要害虫的杀虫效果和在茶树叶片上的降解动态试验结果.上述七种拟除虫菊酯类农药对鳞翅目茶树害虫的幼虫都具有极高的毒力,但对其他害虫的活性谱则表现有差异.它们在茶树芽梢上的降解速率常数为0.20—0.28天^-1,在茶树上的半衰期为2.5—3.5天,明显较有机磷农药稳定.在影响降解的因素中,挥发、热分解、雨水淋洗的作用不大,由茶梢生长稀释所起的作用较为明显.鲜叶中的农药残留在加工过程中的降解率为15—45%,平均20%,远低于有机磷农药.成茶中的残留农药在泡茶过程中由于他们的低水溶性,因此浸出率很低,一般仅有1—4.5%.     

Sustainable intensification of crop residue exploitation for bioenergy: Opportunities and challenges

Crop residue exploitation for bioenergy can play an important role in climate change mitigation without jeopardizing food security, but it may be constrained by impacts on soil organic carbon (SOC) stocks, and market, logistic and conversion challenges. We explore opportunities to increase bioenergy potentials from residues while reducing environmental impacts, in line with sustainable intensification. Using the case study of North Rhine‐Westphalia in Germany, we employ a spatiotemporally explicit approach combined with stakeholder interviews. First, the interviews identify agronomic and environmental impacts due to the potential reduction in SOC as the most critical challenge associated with enhanced crop residue exploitation. Market and technological challenges and competition with other residue uses are also identified as significant barriers. Second, with the use of agroecosystem modelling and estimations of bioenergy potentials and greenhouse gas emissions till mid‐century, we evaluate the ability of agricultural management to tackle the identified agronomic and environmental challenges. Integrated site‐specific management based on (a) humus balancing, (b) optimized fertilization and (c) winter soil cover performs better than our reference scenario with respect to all investigated variables. At the regional level, we estimate (a) a 5% increase in technical residue potentials and displaced emissions from substituting fossil fuels by bioethanol, (b) an 8% decrease in SOC losses and associated emissions, (c) an 18% decrease in nitrous oxide emissions, (d) a 37% decrease in mineral fertilizer requirements and emissions from their production and (e) a 16% decrease in nitrate leaching. Results are spatially variable and, despite improvements induced by management, limited amounts of crop residues are exploitable for bioenergy in areas prone to SOC decline. In order to sustainably intensify crop residue exploitation for bioenergy and reconcile climate change mitigation with other sustainability objectives, such as those on soil and water quality, residue management needs to be designed in an integrated and site‐specific manner.     

旧石器遗址出土烧骨的技术分析及其对考古学的启示

烧骨常见于各类旧石器时代遗址中,作为用火残留物的一类,烧骨对研究人类用火行为有着极为重要的意义,而目前国内针对烧骨的研究工作开展得尚不够深入。本文通过介绍目前烧骨研究领域中若干种主流的分析手段及其在考古学上的应用,以求能进一步完善国内关于旧石器时代人工用火的研究框架,同时希望能对中国古人类用火能力的相关研究提供有益的借鉴。     

三江平原湿地开垦对土壤氨基糖积累特征的影响

微生物残体在土壤有机质的形成和稳定过程中发挥着重要作用,但湿地开垦对土壤微生物残体积累特征的影响尚不清楚。本研究以三江平原小叶章湿地为对象,采集原始自然湿地和开垦改种豆科作物后不同耕作年限(5年、10年和25年)的土壤,以氨基糖为微生物残体的标识物,探讨湿地开垦对土壤微生物残体积累特征的影响。结果表明: 自然湿地开垦为农田后显著降低了土壤中氨基糖的含量,且随着开垦年限的增加,氨基糖的损失比例也增加。与自然湿地相比,开垦25年后土壤中的氨基葡萄糖、氨基半乳糖和胞壁酸含量分别下降38.0%、38.1%和35.9%,且在开垦最初5年中细菌来源的胞壁酸下降速率(25.8%)远高于真菌来源的氨基葡萄糖(14.9%),说明短期内湿地开垦对细菌的影响较真菌更加迅速。湿地开垦为农田5、15和25年后,土壤氨基糖总量分别下降21.1%、34.0%和38.0%;同时,氨基糖总量占土壤有机质的比例也受到湿地开垦的显著影响,由自然湿地中的4.8%降至开垦25年后的4.4%。这说明长期湿地开垦加速了土壤有机质中微生物来源有机组分的分解转化,进而改变土壤有机质的组成。这些变化将影响湿地生态系统中土壤有机质的长期稳定和功能演变。     

Soil nitrous oxide emissions following crop residue addition: a meta‐analysis

Annual production of crop residues has reached nearly 4 billion metric tons globally. Retention of this large amount of residues on agricultural land can be beneficial to soil C sequestration. Such potential impacts, however, may be offset if residue retention substantially increases soil emissions of N₂O, a potent greenhouse gas and ozone depletion substance. Residue effects on soil N₂O emissions have gained considerable attention since early 1990s; yet, it is still a great challenge to predict the magnitude and direction of soil N₂O emissions following residue amendment. Here, we used a meta‐analysis to assess residue impacts on soil N₂O emissions in relation to soil and residue attributes, i.e., soil pH, soil texture, soil water content, residue C and N input, and residue C : N ratio. Residue effects were negatively associated with C : N ratios, but generally residue amendment could not reduce soil N₂O emissions, even for C : N ratios well above ca. 30, the threshold for net N immobilization. Residue effects were also comparable to, if not greater than, those of synthetic N fertilizers. In addition, residue effects on soil N₂O emissions were positively related to the amounts of residue C input as well as residue effects on soil CO₂ respiration. Furthermore, most significant and stimulatory effects occurred at 60–90% soil water‐filled pore space and soil pH 7.1–7.8. Stimulatory effects were also present for all soil textures except sand or clay content ≤10%. However, inhibitory effects were found for soils with >90% water‐filled pore space. Altogether, our meta‐analysis suggests that crop residues played roles beyond N supply for N₂O production. Perhaps, by stimulating microbial respiration, crop residues enhanced oxygen depletion and therefore promoted anaerobic conditions for denitrification and N₂O production. Our meta‐analysis highlights the necessity to connect the quantity and quality of crop residues with soil properties for predicting soil N₂O emissions.     

The influence of PAMAM dendrimers surface groups on their interaction with porcine pepsin

In this study the ability of three polyamidoamine (PAMAM) dendrimers with different surface charge (positive, neutral and negative) to interact with a negatively charged protein (porcine pepsin) was examined. It was shown that the dendrimer with a positively charged surface (G4 PAMAM-NH₂), as well as the dendrimer with a neutral surface (G4 PAMAM-OH), were able to inhibit enzymatic activity of pepsin. It was also found that these dendrimers act as mixed partially non-competitive pepsin inhibitors. The negatively charged dendrimer (G3.5 PAMAM-COOH) was not able to inhibit the enzymatic activity of pepsin, probably due to the electrostatic repulsion between this dendrimer and the protein. No correlation between changes in enzymatic activity of pepsin and alterations in CD spectrum of the protein was observed. It indicates that the interactions between dendrimers and porcine pepsin are complex, multidirectional and not dependent only on disturbances of the secondary structure.