Tertiary structure in N-linked oligosaccharides

Distance constraints derived from two-dimensional nuclear Overhauser effect measurements have been used to define the orientation of the Man alpha 1-3Man beta linkage in seven different N-linked oligosaccharides, all containing the common pentasaccharide core Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc beta 1-4GlcNAc. Conformational invariance of the Man alpha 1-3Man beta linkage was found for those structures bearing substitutions on the Man alpha 1-3Man beta antenna. However, the presence of either a GlcNAc residue in the beta 1-4 linkage to Man beta ("bisecting GlcNAc") or a xylose residue in the beta 1-2 linkage to Man beta of the trimannosyl core was found to generate conformational transitions that were similar. These transitions were accompanied by characteristic chemical shift perturbations of proton resonances in the vicinity of the Man alpha 1-3Man beta linkage. Molecular orbital energy calculations suggest that the conformational transition between the unsubstituted and substituted cores arises from energetic constraints in the vicinity of the Man alpha 1-3Man beta linkage, rather than specific long-range interactions. These data taken together with our previous results on the Man alpha 1-6Man beta linkage [Homans, S. W., Dwek R. A., Boyd, J., Mahmoudian, M., Richards, W. G., & Rademacher, T. W. (1986) Biochemistry 25, 6342] allow us to discuss the consequences of the modulation of oligosaccharide solution conformations.     

The beta 1----2-D-xylose and alpha 1----3-L-fucose substituted N-linked oligosaccharides from Erythrina cristagalli lectin. Isolation, characterisation and comparison with other legume lectins

The carbohydrate moieties of Erythrina cristagalli lectin were released as oligosaccharides by hydrazinolysis, followed by N-acetylation and reduction with NaB3H4. Fractionation of the tritium-labelled oligosaccharide mixture by Bio-Gel P-4 column chromatography and high-voltage borate electrophoresis revealed that it is composed of five neutral oligosaccharides. Structural studies by sequential exoglycosidase digestion in combination with methylation analysis and two-dimensional 1H-NMR showed that the major component was the fucose-containing heptasaccharide Man alpha 3(Man alpha 6)(Xyl beta 2)Man beta 4GlcNAc beta 4(Fuc alpha 3)GlcNAcol. This is the first report of such a structure in plant lectins. Small amounts of the corresponding afucosyl hexasaccharide were also identified, as well as three other minor components. The structure of the heptasaccharide shows the twin characteristics of a newly established family of N-linked glycans, found to date only in plants. The characteristics are substitution of the common pentasaccharide core [Man alpha 3(Man alpha 6)Man beta 4GlcNAc beta 4GlcNAc] by a D-xylose residue linked beta 1----2 to the beta-mannosyl residue and an L-fucose residue linked alpha 1----3 to the reducing terminal N-acetylglucosamine residue. The oligosaccharide heterogeneity pattern for Erythrina cristagalli lectin was also found for the lectins from four other Erythrina species and the lectins of two other legumes, Sophora japonica and Lonchocarpus capassa.     

高原低氧对机体无氧代谢阈值的影响

为了探讨高原低氧对机体无氧代谢阈值(AT)的影响,本研究采用Wasserman无创性方法,分别测定了11名新兵在平原(四川淮口,海拔500m)和经空运进驻高原 (西藏错那,海拔4370m)后的第3、5、7和14天的AT。结果表明:新兵进驻高原后AT由平原的813.6±147.4kg·m/min降低到395.5±194.5 kg·m/min(P<0.01);高原低氧引起AT的降低幅度与受试者平原AT的高低呈正相关(r=0.933,P<0.01);进驻高原后第3、5、7天AT维持在较低水平,随后呈上升趋势。但移居高原1年战士的AT仍低于平原水平(P<0.05)。提示,高原低氧能够显著地降低机体的AT,并且AT越高的个体进驻高原后受低氧环境的影响程度越大。     

Plant growth regulation with triazoles of the dioxanyl type

The plant growth retarding activities of several dioxanylalkyl and dioxanylalkenyl triazoles were determined in seedlings of barley, rice, and oilseed rape. Out of these groups some substances proved to be among the most efficient growth retardants known. The compound 1-(4-trifluormethyl)-2-(1,2,4-triazolyl-(1))-3-(5-methyl-1,3-dioxan-5-yl)-propen-3-ol was investigated more closely. Shoot growth is reduced more intensively than root growth by this compound. At lower dosages root growth may even be stimulated. The action of this retardant can be antagonized by gibberellin A₃ and byent-kaurenoic acid. It is suggested that its main biochemical action is to block the reactions that lead froment-kaurene toent-kaurenoic acid in the course of gibberellin biosynthesis.     

白翅叶蝉Empoasca subrufa Melichar的研究

白翅叶蝉是福建省水稻的重要害虫,苗期受害严重者,整片稻苗苍白,甚至枯死;早稻孕穗、抽穗期常大量发生为害,影响谷粒饱满度,造成减产。福州和闽侯地区一年发生4代,部分5代。成虫越冬。冬季日平均温度达11℃以上时仍能取食为害。春季成虫侵入稻田,4月下旬前后大量产卵,5月中旬虫数激增,5月下旬或6月初达到高峰。早稻收割时由于农事活动引致若虫大量死亡。晚稻田于8、9月虫数较多,但危害不如早稻严重。10月中旬以后成虫逐渐离开稻田,迁往越冬场所。 寄主植物幼嫩茂密和较大湿度的小生境有利于白翅叶蝉的发育繁殖。大发生的气候因子主要是春季多雨。适宜的温湿度范围为温度20—25℃,相对湿度85—90%。 DDT单独使用或DDT与666混用防治白翅叶蝉都能收到满意的效果。早稻秧田宜在播种后两周施药防治;本田于5月中旬虫口密度开始增长之际施药,亦能抑制为害。冬季小麦出土以前清除田边杂草,也是一项有效的防治措施     

Synthetic glycosylation of peptides using unprotected saccharide β-glycosylamines

Glycopeptides can be valuable tools in determining the influence of carbohydrate moieties on the intrinsic properties of glycoproteins. However, glycopeptides of sufficient quantity and purity are as yet not readily available from biological sources. The chemical coupling of a -glycosylamino group of an unprotected carbohydrate with an activated aspartic acid residue of an unprotected peptide is a simple method for synthesizing asparagine-linked glycopeptides. In this report we demonstrate that the use of this method is not restricted to -glycosylamines of simple monosaccharides or short aspartic acid-containing pentapeptides. This is illustrated by the syntheses of several glycopentapeptides containingN,N-diacetylchitobiose, a glutamine-linked glycopentapeptide containing a biantennary complex oligosaccharide, and glycosylated variants of two analogs of a polypeptide hormone, atriopeptin, containingN,N-diacetylchitobiose.Abbreviations Ac acetyl - Bzl benzyl - DMF dimethylformamide - Fmoc 9-fluorenylmethoxycarbonyl - Fuc fucose - Gal galactose - GlcNAc N-acetylglucosamine - HBTU O-benzotriazol-1-yl-N,N,N,N-tetramethyluroniumhexa-fluorophosphate - HOBt 1-hydroxybenzotriazole - Man mannose - m/z mass/charge - NMR nuclear magnetic resonance - Xyl xylose - Z benzyloxycarbonyl; unless otherwise specified, amino acids are abbreviated using their one-letter codes.