Inhibition of aldose reductase by dihydroflavonols inEngelhardtia chrysolepis and effects on other enzymes

Astilbin and neoastilbin, dihydroflavonol rhamnosides fromEngelhardtia chrysolepis, showed potent inhibition of lens aldose reductase. Kinetic analysis showed astilbin exhibited uncompetitive inhibition against bothdl-glyceraldehyde and NADPH. These taxifolin glycosides were selective inhibitors of aldose reductase with no inhibition of NADH oxidase.     

乳酸菌亚硝酸还原酶代谢调控研究进展

利用亚硝酸盐还原酶(Nir)降解发酵食品中产生的亚硝酸盐,是应对亚硝酸盐污染的根本对策。研究乳酸菌亚硝酸盐还原酶的分子调控机制,为进一步揭示乳酸菌nir操纵子调控系统的功能及模式元件的组合、新的调控模型和信号传导的分子调控机制奠定基础,对加快寻找安全有效的亚硝酸盐生物降解法,进而保障国家的食品安全具有重要意义。     

香椿芽硝酸盐含量与硝酸还原酶活性的研究

选择安徽歙县、四川遂宁、江西九连山、河南南阳、河南焦作、河北石家庄、河南郑州、山东泰安等8个种源的香椿芽为实验材料,对其硝酸盐含量、硝酸还原酶活性及其相关关系进行了比较研究．结果表明：不同种源香椿芽硝酸盐含量和硝酸还原酶活性不同．硝酸盐含量较低的为江西九连山、河南焦作和安徽歙县种源,是较为理想的食用种源,在四个不同采摘时期,硝酸还原酶活性较高的几乎都是江西九连山种源和河南焦作种源,其余种源的硝酸还原酶活性相对较低．硝酸盐含量和硝酸还原酶活性之间的关系可用相关方程来拟合,除采摘的第一个时期外,后三个时期不同种源香椿芽硝酸盐含量和硝酸还原酶活性显著或极显著负相关．     

Site-directed mutagenesis reveals new and essential elements for iron-coordination of the sulfur oxygenase reductase from the acidothermophilic Acidianus tengchongensis

Previous study on refolding of sulfur oxygenase reductase (SOR) inclusion bodies from recombinant Escherichia coli showed that iron was critical to the activity of the SOR from Acidianus ambivalens. In this study, enzymatic assays showed that 2,2′-Dipyridyl, Tiron and 8-hydroxyquinoline, which are specific for chelating ferrous or ferric ions, strongly inhibited the activity of SOR from A. tengchongensis, suggesting that iron atom is essential for SOR activity. Alignment of several functionally identified SORs and SOR-like sequences from genome database revealed a conserved, putative iron binding motif, H⁸⁶-X₃-H⁹⁰-X _n -E¹¹⁴-X _n -E¹²⁹ (numbering according to the Acidianus tengchongensis SOR sequence). Three mutants of SOR were generated by site-directed mutagenesis of H₈₆, H₉₀ and E₁₂₉ into phenylalanine or alanine residue in this study. Circular dichroism spectrum determination indicated that there was no change of the secondary structures of mutant SORs, H⁸⁶F, H⁹⁰F and E¹²⁹A, but all mutants were completely inactive. Through determination of iron contents we found that SOR mutants of H⁸⁶F, H⁹⁰F and E¹²⁹A completely or partially lost iron, while mutants of C³¹S, C¹⁰¹S, and C¹⁰⁴S (generated in a previous study) did not. This result indicated that H⁸⁶, H⁹⁰ and E¹²⁹ but not C³¹, C¹⁰¹, and C¹⁰⁴ were involved in binding to iron atom. Based on this and previous studies, it is proposed that the conserved motifs, C³¹-X _n -C¹⁰¹-X₂-C¹⁰⁴ and H⁸⁶-X₃-H⁹⁰-X₂₃-E¹¹⁴-X₁₄-(E/D)¹²⁹, are respectively for sulfur and molecular oxygen binding and activation. These two conserved motifs are essential elements for the SOR activity. Supported by National Natural Science Foundation of China (Grant Nos. 30670018, 30621005) and State Key Basic Research and Development Program of China (Grant No. 2004CB719602)     

香根草对重金属镉的积累及耐性研究

通过香根草的水溶液培养,研究了不同浓度的镉(Cd)对香根草的生理和生态的影响.结果表明:香根草富集的Cd主要被累积在根内,最高富集系数达到24.06%.溶液Cd浓度与香根草根内Cd的累积量显著正相关(r=0.987 4),与根的耐性指数呈显著负相关(r=-0.943 6).低浓度Cd(≤1 mmol.L-1)处理使根系活力和硝酸还原酶(NR)活力随时间呈现先升后降的趋势,中、高浓度Cd(≥1.5 mmol.L-1)处理使根系活力呈显著下降的趋势,且浓度越高,下降幅度越大.化学形态分析表明,在香根草体内Cd的NaCl提取态占绝对优势,在根和茎叶内的平均占52.06%和64.03%.可以认为香根草在Cd胁迫下其氮代谢、呼吸作用,植物的生长发育受到一定程度抑制,但其对Cd仍具有较强的耐性和富集能力.     

大肠杆菌巴豆甜菜碱还原酶基因缺失菌株的构建

报道了体外构建caiA基因缺失的带有卡那霉素抗性基因的5．2kb线状DNA分子,以此转化大肠杆菌JM83和BL21(DE3)株,借助于体内DNA同源重组,定向敲除了大肠杆菌中的巴豆甜菜碱还原酶编码基因caiA。经遗传稳定性实验、聚合酶链反应(PCR)以及Southern鉴定,表明所获得的JM83转化子22号和BL21(DE3)转化子4号确为caiA基因缺失突变株;酶活分析结果表明,22号和4号转化子均丧失了巴豆甜菜碱还原酶活性。     

两类脂肪酸合酶中酮酰还原酶的结构、功能和药物开发前景

自然界中脂肪酸合酶（FAS）以FASⅠ和FASⅡ两种形式存在。存在于动物中的FASⅠ是由多活性中心构成的复合酶,存在于植物和细菌中的FASⅡ则是由多个独立蛋白构成的酶体系。FASⅠ和FASⅡ中催化酮酰基团还原的酶有一定同源性,酶催化动力学和酶抑制动力学的性质相似,因分子量过大,目前尚无详细的FASⅠ空间结构信息。通过比较两种类型FAS中酮酰还原酶结构与功能的异同,进一步了解FASⅠ的结构与功能。对两种不同进化程度和存在形式的同源酶进行比较研究,将有得提示复合酶的结构与功能,并得寻找新型特异性蛋白抑制剂,为新药开发提供先导化合物,具有十分重要的理论意义和应用价值。     

春小麦幼苗硝酸还原酶活性与品种抗旱性的关系

报道了PEG溶液渗透胁迫下春小麦幼苗的NR活性及含氮物质的变化,并对NR活性作为评定春小麦品种抗旱性的指标进行了探讨。结果表明,抗旱性强的品种在无胁迫时NR活性一般较低,在胁迫时,酶活下降幅度较小,SI亦较小;抗旱性弱的品种具有相反的特征。说明春小麦幼苗NR活性与品种的抗旱性有着一定的关系。