Effects of net charge on the hydrogen-deuterium exchange parameters of lysozyme.

Possible effects of changes in net charge on protein hydrogen exchange rates were investigated by desalting hen egg-white lysozyme, which allowed its net charge to increase with decreasing pH in the acid region. Chloride ion-binding ratios, expressed as ratios of free to total Cl^?, were measured with a chloride-specific electrode at pH 5 on a 2.4% solution of a five-time-desalted product. This ratio was used to show a 97% reduction of the 11% Cl^? present in a commercial lysozyme preparation upon three passes of the enzyme through a column of ion-retardation resin. Net charges on the purified product were assigned from a combination of electrophoretic mobility and proton titration data gathered under minimal ionic strength conditions. The net charge on the desalted product increased by 1.64 units between pH 5.0 and 3.0. Hydrogendeuterium exchange studies on the purified lysozyme in D₂O were obtained using the near-infrared region of a Cary 14R spectrophotometer. The rate-pD profile for k₂, the rate constant for the intermediate class of exchanging hydrogens, showed a decrease in the apparent pD of minimum exchange rate of 0.3 units, when compared to that obtained earlier in 0.2 m added NaCl. However, the rate of exchange at pD minimum and the number of hydrogens in the class remained largely unaffected. A similar shift was observed for the rate-pD profile of the class 1 hydrogens. Thus, the effect of an increase in net positive charge is to shift the rate-pD profile to a lower pD. Moreover, the effect extended to the interior peptide hydrogens of this globular protein. Consequently, the exchange rates of all the observable hydrogens are altered by the net charge changes, and the effect appeared uniform. The shift can be accounted for quantitatively by applying electrostatic interaction terms to the acid and base catalytic constants characterizing the exchange process. The calculated electrostatic interaction factors in minimal salt and 0.2 m added NaCl were found to be 29 and 18% lower, respectively, than those obtained theoretically. Therefore, under conditions where changes in net charge may occur for a globular protein, the effect on hydrogen exchange rates can be estimated fairly well theoretically, especially at moderate ionic strengths.     

Flavonoids and tannins of Acacia species

The heartwoods of Acacia giraffae and A. galpinii were selected from South African Acacias as representative of those with abnormally high and minimal tannin contents respectively. A. galpinii contains amongst other analogues, the first natural (+)-2,3-trans-3,4-trans-teracacidin (7,8,4′-trihydroxy-flavan-3,4-diol and novel 3-O-methyl-, 7,8-di-O-methyl- and 7,8,4′-tri-O-methylflavonol analogues. (−)-2,3-cis-3,4-cis-Melacacidin (7,8,3′,4′-tetrahydroxyflavan-3,4-diol) is also present, but tannins are absent. By contrast, from the large excess of leueofisetinidin tannins which characterizes the wood of A. giraffae, only (+)-catechin, (+)-2,3-trans-3,4-trans-leucofisetinidin (7,3′,4′,trihydroxyflavan-3,4-diol and all-trans-(+)-leueofisetinidin-(+)-catechin could be isolated.     

Site Variation in Littoral Periphyton Populations: Correlation and Regression with Environmental Factors

Over a six month period, littoral periphyton communities on vertically oriented glass slides were quantitatively sampled from four stations in Elk Lake, British Columbia. Correlation and multiple regression analyses were employed to assess the temporal interrelationships between 15 environmental variables, concurrently measured, and the periphyton populations, expressed as total cell counts and species diversity, for the complete data set of each station. At all stations there was a statistically significant increase in total cell populations with increasing length of slide exposure; positive correlations also occurred with pH, temperature, nitrite, nitrate and copper, while negative ones occurred with oxygen, orthophosphate and hardness (magnesium and total). At all but one station there was a significant decrease in species diversity with increasing slide exposure duration, a decrease attributed to the simultaneous increase in standing crop resulting in intensified competition for diminishing substrate area suitable for cell colonization. Multiple stepwise regression analyses demonstrated that greater than 80% of the variation in periphyton total cells at all four stations could be reliably predicted or described in terms of length of slide exposure, phosphate (ortho and total), and hardness (calcium and total). On the other hand, exposure duration and total cell populations were the most important variables associated with changes in species diversity at three of the four stations. In general, correlations and regressions between standing crop and environmental variables were more statistically reliable and consistent between stations than comparable analyses with species diversity. Use of multiple regression and correlation disclosed the importance of small, non statistically significant variation in ecologically relevant variables and permitted objective comparison of stations.     

早产儿语言发展的影响因素及其干预对策

早产儿的语言发展受到多种因素的影响,可能导致他们在词汇、语法、语音等方面出现发展滞后或障碍。本文首先简述了影响早产儿语言发展的生物学和环境因素的研究进展,其中生物学因素包括早产程度、体重和性别、新生儿发病率和疾病严重程度等,环境因素则包括新生儿重症监护室的环境、家庭中的语言环境和社会因素等。在明确这些影响因素的基础上,本文强调了早期评估和早期干预是优化早产儿语言发育效果的关键步骤,并分析了具体的干预对策,例如生理和神经干预、优化新生儿重症监护室（NICU）环境、增强家庭语言互动、多学科合作和社会支持等。此综述旨在探讨影响早产儿语言发展的各种因素,并总结出有效的早期干预措施,为其提供更为全面的语言发展支持。     

Effects of Luteolin on Human Breast Cancer Using Gene Expression Array: Inferring Novel Genes

Taraxacum officinale (dandelion) is often used in traditional Chinese medicine for the treatment of cancer; however, the downstream regulatory genes and signaling pathways mediating its effects on breast cancer remain unclear. The present study aimed to explore the effects of luteolin, the main biologically active compound of T. officinale, on gene expression profiles in MDA-MB-231 and MCF-7 breast cancer cells. The results revealed that luteolin effectively inhibited the proliferation and motility of the MDA-MB-231 and MCF-7 cells. The mRNA expression profiles were determined using gene expression array analysis and analyzed using a bioinformatics approach. A total of 41 differentially expressed genes (DEGs) were found in the luteolin-treated MDA-MB-231 and MCF-7 cells. A Gene Ontology analysis revealed that the DEGs, including AP2B1, APP, GPNMB and DLST, mainly functioned as oncogenes. The human protein atlas database also found that AP2B1, APP, GPNMB and DLST were highly expressed in breast cancer and that AP2B1 (cut-off value, 75%) was significantly associated with survival rate (p = 0.044). In addition, a Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that the DEGs were involved in T-cell leukemia virus 1 infection and differentiation. On the whole, the findings of the present study provide a scientific basis that may be used to evaluate the potential benefits of luteolin in human breast cancer. Further studies are required, however, to fully elucidate the role of the related molecular pathways.     

玉米联合固氮菌Kosakonia radicincitans GXGL-4A的分离鉴定与固氮特性研究

【目的】固氮微生物是生物固氮的主体,其菌种的选育更是生物固氮研究的基础。本实验室分离鉴定出一株新的固氮菌,并对其固氮相关活性进行初步研究。【方法】固氮菌采用Ashby无氮培养基进行分离纯化。通过形态特征分析、生理生化特征分析、16S r RNA基因序列分析和基因组扫描对固氮菌进行鉴定。利用靛酚蓝-分光光度法检测固氮菌的泌铵能力。固氮酶活性的测定使用乙炔还原法。【结果】从玉米根部分离到一株固氮菌株GXGL-4A,菌体短杆状,大小约为1.5μm×0.5μm,单个或常见2个菌体细胞串联在一起,革兰氏染色结果为阴性。16S r RNA基因序列分析结果表明该菌株与Kosakonia oryzae Fo8A1d 16S r RNA基因序列有95%的相似性,结合形态特征、生理生化特征和基因组扫描,将其命名为K.radicincitans GXGL-4A。对其进行固氮基因nif H的检测,经PCR扩增得到预期的296 bp条带;采用靛酚蓝-分光光度法,测得发酵液中铵态氮含量为2.5 mg/L,表明该菌株具有较好的泌铵能力。乙炔还原法测其固氮酶活性,以乙烯生产量表示,结果显示GXGL-4A菌株在无氮培养基上能够有效地还原乙炔,达到232.94 nmol C2H4/(m L·h)。【结论】菌株GXGL-4A是一株可较好地分泌铵的新的固氮菌,具有很好的研究价值。     

生物启发的细菌表面人造矿物壳:通过仿生矿化保护活细胞

【目的】生物启发的细菌表面仿生矿化人造矿物壳被用于保护活细胞。【方法】将细菌限制在坚固而完整的矿物壳中,有限的物理空间和物质交换使其暂时进行休眠,降低长期保存期间的活力损失以及提高在各种极端环境中的生存能力,并且能够通过酸去除矿物壳而重新激活细菌。【结果】相较于未仿生矿化的细菌(EcN),矿化细菌(EcN@CaCO₃)在32 d的储存实验中活力最高提升262倍;在pH 2.5的强酸环境中存活率提高837倍;在pH 12.0的强碱环境中存活率提高171倍;在80 ℃的高温条件下存活率提高59.1倍;甚至在抗生素溶液中,EcN@CaCO₃中细菌的存活率是EcN的729.7倍。【结论】本研究利用仿生矿化提高了细菌的保存稳定性,使其能在酸刺激下去除涂层恢复活性,也能在极端环境下保留细菌的活力,为微生物在环境生态、食品制造和生物医药等领域的应用提供研究基础。     

水土保持林土壤改良效益评价研究

森林效益评价是目前林业研究的热点,也是难点问题,通过评价水土保持林土壤改良效益,对效益评价的方法和思路进行了探索。指出水土保持林土壤改良效益指标体系的总目标层为效益评价综合指数,准则层包括土壤肥力、抗蚀性能和抗冲性能３个方面,指标层由水稳性团聚体含量、有机质含量、土壤酶活性、ｐＨ值、平均重量直径、团聚度、分散率、土壤硬度和渗透系数构成。在计算效益评价综合指数时,首先要对各项指标的实测数据进行处理,