低聚木糖对两歧双歧杆菌的增殖

以酶解低聚木糖为碳源，在严格厌氧条件下增殖两歧双歧杆菌。研究表明，低聚木糖可有效增殖两歧双歧杆菌，两歧双歧杆菌对该糖的转化率与对葡萄糖的相近。将低聚木糖在浓度为5.0-10g/L的范围内增加其初始浓度，可提高双歧杆菌的菌体浓度和增殖速率，低聚木糖对两歧双歧杆菌和青春双歧杆菌的双株混合培养效果明显优于单株培养，其功能完全符合人体的生理特点，适宜于低聚木糖在人体内自然增殖双歧杆菌菌群。     

Role of <Emphasis Type="Italic">N</Emphasis>-linked polymannose oligosaccharides in targeting glycoproteins for endoplasmic reticulum-associated degradation

Misfolded or incompletely assembled multisubunit glycoproteins undergo endoplasmic reticulum-associated degradation (ERAD) regulated in large measure by their N-linked polymannose oligosaccharides. In this quality control system lectin interaction with Glc₃Man₉GlcNAc₂ glycans after trimming with endoplasmic reticulum (ER) -glucosidases and -mannosidases sorts out persistently unfolded glycoproteins for N-deglycosylation and proteolytic degradation. Monoglucosylated (Glc₁Man₉GlcNAc₂) glycoproteins take part in the calnexin/calreticulin glucosylation-deglucosylation cycle, while the Man₈GlcNAc₂ isomer B product of ER mannosidase I interacts with EDEM. Proteasomal degradation requires retrotranslocation into the cytosol through a Sec61 channel and deglycosylation by peptide: N-glycosidase (PNGase); in alternate models both PNGase and proteasomes may be either free in the cytosol or ER membrane-imbedded/attached. Numerous proteins appear to undergo nonproteasomal degradation in which deglycosylation and proteolysis take place in the ER lumen. The released free oligosaccharides (OS) are transported to the cytosol as OS-GlcNAc₂ along with similar components produced by the hydrolytic action of the oligosaccharyltransferase, where they together with OS from the proteasomal pathway are trimmed to Man₅GlcNAc₁ by the action of cytosolic endo--N-acetylglucosaminidase and -mannosidase before entering the lysosomes. Some misfolded glycoproteins can recycle between the ER, intermediate and Golgi compartments, where they are further processed before ERAD. Moreover, properly folded glycoproteins with mannose-trimmed glycans can be deglucosylated in the Golgi by endomannosidase, thereby releasing calreticulin and permitting formation of complex OS. A number of regulatory controls have been described, including the glucosidase-glucosyltransferase shuttle, which controls the level of Glc₃Man₉GlcNAc₂-P-P-Dol, and the unfolded protein response, which enhances synthesis of components of the quality control system.Received 26 January 2004; accepted 25 February 2004     

糖复合物的生物应用

糖类化合物是一类很重要的生物大分子,它在细胞膜表面通过形成各种复合物参与许多重要的生理活动。主要讨论了近几年糖类复合物在药物靶向传递及肿瘤成像/检测等方面的研究进展,综述了叶酸、寡糖等作为靶向基团的药物靶向传递体系,同时探讨了各种糖类复合物在细胞成像及生物检测方面的应用,指出了未来糖化学的发展前景。     

不同温度热解酸化蔗糖制备低聚焦糖

为拓展热解酸化蔗糖制备低聚焦糖的应用领域,分别考察了不同温度下干法与湿法制备的低聚焦糖的pH值、特征吸收、褐变程度、糖含量、抗氧化性,并分析了低聚焦糖的主要成分和热稳定性.结果表明:随着温度升高,干法工艺制备的低聚焦糖的pH值先升高后缓慢降低,湿法工艺制备的则逐渐降低;干法工艺制备的低聚焦糖的特征吸收及褐变程度均上升,湿法工艺制备时则在160℃达到最强,分别为3.151和2.128;两种工艺制备的低聚焦糖的总糖含量逐渐减少,还原糖含量先上升后下降,抗氧化性增强;低聚焦糖主要成分为蔗糖、蔗果三糖等低聚糖,以及少量的葡萄糖、果糖等;低聚焦糖的热裂解产物主要有呋喃、呋喃酮、吡唑、吡咯烷、醛、烯和酸酐类.     

微生物肥料科学研究中几个热点问题

微生物肥料作为一项新的农业措施，在提供绿色食品、保护农业生态环境以及发展高产、优质、高效农业中的作用业已引起国内外学者的普遍重视，为促进我国微生物肥料基础和应用基础研究，作者提出微生物肥料科学研究中值得深入探讨的几个热点问题，如开展寡糖在植物生长中的调节功能与利用研究，应用微生态学与PCPR理论来促进微生物肥料产业的发展，把微生物肥料产业的发展与资源有效利用、环境保护和食品安全等相联系。     

胡萝卜中寡糖的提取方法研究

文章研究了三种从胡萝卜中提取寡糖的方法,较佳的工艺是:用乙醇-甲醇两次抽提法,先用乙醇和沸甲醇抽提单糖,再用甲醇抽提寡糖。这样可以使寡糖中单糖的含量尽可能少,同时也大大降低了寡糖中杂质的含量。抽提出来的寡糖先用氯仿-正丁醇法脱蛋白质,再用粉末活性炭脱色。通过凝胶层析对其进行分离纯化,用苯酚-硫酸法测其含量。     

Triple arginines in the cytoplasmic tail of endomannosidase are not essential for type II membrane topology and Golgi localization

Endomannosidase is a Golgi-localized endoglycosidase, which provides an alternate glucosidase-independent pathway of glucose trimming. Using a protease protection assay we demonstrated that Golgi-endomannosidase is a type II membrane protein. The first 25 amino acids of this protein, containing the cytoplasmic tail and the transmembrane domain, were sufficient for Golgi retention of fused reporter proteins alpha1-antitrypsin or green fluorescent protein. However, shortening or deletion of the transmembrane domain prevented Golgi localization, while lengthening it partially reduced Golgi retention of the enzyme. Substitution of the highly conserved positively charged amino acids within the cytoplasmic tail had neither an effect on type II topology nor on the inherent Golgi localization of the enzyme. In contrast, cytoplasmic tail-deleted rat endomannosidase possessed an inverted topology resulting in endoplasmic reticulum mislocalization. Thus, proper topology rather than the presence of positively charged amino acids in the cytoplasmic tail is critical for Golgi localization of rat endomannosidase.     

The surface glycopeptidolipids of mycobacteria: structures and biological properties

One of the most important opportunistic pathogens associated with acquired immunodeficiency syndrome (AIDS) is the M. avium complex. M. avium infections are found in up to 70% of individuals in advanced stages of AIDS. It is apparent that M. avium can replicate in host macrophages and persist for long periods. This group of mycobacteria are distinguished by the presence of unique, highly antigenic, surface-located lipids known as the glycopeptidolipids (GPLs). The GPLs are the chemical basis of the 31 distinct serovars of the M. avium complex, and have also been identified in some other species. The M. avium lipids are immunosuppressive and can induce a variety of cytokines that affect general host responses. Despite extensive chemical characterization of the structures of these GPLs, much work is needed to elucidate the molecular mechanism involved in this complex glycosylation pathway and its genetic basis. The challenges for the future lie in explaining the roles of these copious products in the intracellular life and infectivity of mycobacteria. The intention of our review is to offer a concise account of the structures of the M. avium lipids, their putative roles in the host responses, bacterial physiology and pathogenesis, particularly in immunocompromised patients such as those infected with human immunodeficiency virus (HIV). Advances in chemical synthesis of the various haptenic oligosaccharides are also given to demonstrate how these have helped to define the immunogenic determinants. We believe that future research should involve the creation of conditional mutants defective in these lipids for both functional and biosynthesis studies which will complement biological assays using chemically defined or modified neoglycoconjugates. Received 7 May 2001; received after revision 28 June 2001; accepted 28 June 2001     

魔芋低聚糖降低糖尿病小鼠血糖和胆固醇效应的研究

主要研究魔芋低聚糖对实验性糖尿病小鼠血糖浓度的影响 .先用 5 %四氧嘧啶水溶液腹腔注射(ip)诱发小鼠糖尿病 ,再用不同剂量的魔芋低聚糖水溶液灌胃 (ig) ,先后测定小鼠血糖值及某些血液成分的含量 .实验 2周后结果显示 ,灌服了低、高剂量魔芋低聚糖液的糖尿病小鼠血糖值分别为 1 0 .4 1± 2 .2 3mmol L、9.81± 1 .67mmol L,与未用药的糖尿病组 (1 7.1 7± 3 .89mmol L)比较明显降低 (P <0 .0 1 ) ,同时血液中某些成分的含量改善 .提示魔芋低聚糖有明显的降血糖及改善血液成分的作用 ,为利用其开发降糖保健食品及药品提供了实验依据