细菌中D-氨基酸生物合成及调控作用研究进展

细菌中普遍存在L/D型氨基酸,与L-氨基酸(L-AAs)不同,D-氨基酸(D-AAs)不参与蛋白质合成,而与细胞壁肽聚糖的合成有关,直接影响细菌细胞壁的形状、数量和强度。D-AAs在细菌表征、药物抑菌性、靶标确定等方面具有重要的作用。目前,外源添加D-AAs参与肽聚糖合成的机制已有一些研究进展,其荧光衍生物已应用于细菌可视化,特异性探测细胞壁形成/重塑、细菌生长和细胞形态。但D-AAs如何影响细菌生长及其抗逆性的机制尚未研究清楚。对D-AAs的研究现状进行综述,重点介绍D-AAs在细菌中的生物合成机制和参与细胞壁合成的机制、非典型DAAs对细菌的调控以及在细菌可视化中的应用,并对D-AAs未来研究方向进行了展望。     

细菌鸟氨酸脱羧酶作用的研究进展

多胺是生物体内广泛存在的一类具有多种生物活性的低分子化合物,其合成的关键限速酶是鸟氨酸脱羧酶,鸟氨酸脱羧酶和多胺共同参与生物生长发育等重要生理过程。细菌鸟氨酸脱羧酶在结构上和真核生物略有不同,但是功能类似,其能通过促进多胺的产生发挥对细菌的调节作用。研究发现,细菌鸟氨酸脱羧酶也参与细菌对其他物种的作用,但对人体的作用尚不明确。因此,本文综述了国内外关于细菌鸟氨酸脱羧酶在促进细菌生长、适应环境、抗生素抗性和生物膜形成等方面的作用及相关机制,希望能对细菌鸟氨酸脱羧酶及其作用的后续研究提供一些信息与参考。     

非蛋白氨基酸的生物合成及其生物学作用

解释了蛋白氨基酸和非蛋白氨基酸,并着重论述了非蛋白氨基酸的生物合成及其生物学作用。非蛋白氨基酸的生物合成主要通过基本氨基酸合成后的修饰、代谢及消旋作用产生,其生物学作用主要表现在能合成其他含氮物质、储藏氮和运输氮、储能、组成细菌细胞壁、毒性作用及药物作用等方面。     

水生生物的紫外防护剂——类菌胞素氨基酸

类菌胞素氨基酸(mycosporine-like amino acids, MAAs)是一大类以环己烯酮为基本骨架, 与不同类型氨基酸通过缩合作用形成的水溶性物质。它能在真菌、海洋细菌、蓝藻和真核藻类细胞中合成, 并在海生无脊椎动物和鱼类等生物体内积累, 广泛存在于多种水生生物中。它具有紫外光防护、渗透、繁殖调节及发育保护等功能。本文主要介绍有关类菌胞素氨基酸的分布、结构、生物合成和积累以及生理功能的研究进展。     

体内游离谷氨酰胺的抗氧化作用

作为一种条件必需氨基酸,体内存在的丰富的游离谷氨酰胺具有重要的生理调节功能,尤其在抗氧化反应中发挥对机体的保护作用。游离谷氨酰胺可通过氧化供能、调节信号传递过程中凋亡酶的活性、抑制一氧化氮(NO)合成、参与肿瘤坏疽因子d(TNF-a)诱导的细胞毒性作用、参与合成谷胱甘肽,加速细胞增殖等生理过程减轻氧化压力。谷氨酰胺抗氧化作用的发现可以为癌症、移植手术、免疫功能低下等病人的治疗提供依据。     

c-di-AMP调控细菌生物被膜的形成

细菌生物被膜是细菌持续性致病的重要机制。研究细菌生物被膜的形成和发展可为顽固性细菌感染防治提供新的思路与策略。环二腺苷酸c-di-AMP(Cyclic diadenosine monophosphate)是继c-di-GMP之后在细菌中新发现的一种核苷酸第二信使分子。研究发现,c-di-AMP参与调节细菌多种生理功能,包括细菌生长代谢、生物被膜形成、细胞壁的合成以及细菌毒力因子等。本文综述了c-di-AMP参与调控细菌生物被膜形成的不同方式及其分子机制。鉴于c-di-AMP在调控细菌生物被膜中的重要性,其可作为抗细菌生物被膜感染新药研发的潜在靶点。     

细菌素对产生菌获得生存优势及其诱导合成条件的研究进展

细菌素可以有效抑制其他细菌的生长,是产生菌获得生存优势的重要手段。细菌素使产生菌获得竞争优势基于两个方面:就产生菌自身而言,将细菌素吸附于细胞表面可能增强细胞表面疏水性,进而对定殖产生正向作用;就目标菌而言,细菌素可以自外而内抑制目标菌生物被膜、细胞壁、细胞膜的合成或破坏其结构完整性,同时还可影响其功能基因的表达。然而,伴随细菌素合成的往往是一簇基因的共同表达,需要一定的非生长相关性能量和物质消耗。因此,为实现细菌素合成的调控,细菌素表达基因的开启受制于细菌素自诱导、共培养诱导和环境因子诱导等一系列条件,以实现细菌素利用效率的最大化。根据细菌素主要的抑菌/杀菌机制,我们展望了细菌素耐受性突变菌株可能具有更强流动性细胞膜和(或)更高效小分子合成途径和(或)细菌素受体突变的特征,并提出了科学使用细菌素的建议。     

水生生物的紫外光防护剂--类菌胞素氨基酸

类菌胞素氨基酸（mycosporine—like amino acids,MAAs）是一大类以环己烯酮为基本骨架,与不同类型氨基酸通过缩合作用形成的水溶性物质。它能在真菌、海洋细菌、蓝藻和真核藻类细胞中合成,并在海生无脊椎动物和鱼类等生物体内积累,广泛存在于多种水生生物中。它具有紫外光防护、渗透、繁殖调节及发育保护等功能。本文主要介绍有关类菌胞素氨基酸的分布、结构、生物合成和积累以及生理功能的研究进展。     

体外法研究猪后肠道对芳香族氨基酸的发酵特性

【目的】采用体外发酵技术探究芳香族氨基酸在猪后肠的发酵特性。【方法】以杜×长×大育肥猪回肠、盲肠和结肠食糜为接种物,接种于10 mmol/L单一氨基酸的培养基中,37 o C培养24 h,测定4、8、12、16和24 h的产气量(GP),采集0 h和24 h样品,测定样品中的氨氮(NH3-N)和微生物蛋白(MCP)浓度,利用变性梯度凝胶电泳技术(DGGE)和Real-time PCR定量技术分析体外培养中参与代谢特定氨基酸的细菌组成及数量。【结果】不同芳香族氨基酸的发酵液中NH3-N和MCP浓度存在极显著差异(P0.01),肠段对GP、NH3-N和MCP影响极显著(P0.01),且芳香族氨基酸与肠段对GP、NH3-N和MCP浓度均存在交互作用(P0.01)。定量PCR表明,芳香族氨基酸和肠段均显著影响发酵液中总菌数量(P0.05)。DGGE分析显示,同一肠段不同芳香族氨基酸组的细菌群落结构具有高度的相似性,其中回肠Phe组和Tyr组、结肠Tyr组和Trp组的相似性分别高达87.9%和80.5%,盲肠和结肠微生物香农指数变化显著(P0.05)。【结论】不同芳香族氨基酸的肠道代谢菌具有差异性,与Trp和Phe相比,Tyr的盲肠和结肠代谢菌多样性较低,与Trp和Tyr相比,Phe更多地合成菌体;特定芳香族氨基酸的不同肠道发酵去向不同,与回肠和盲肠比,结肠中芳香族氨基酸更多地合成菌体。     

趋磁细菌蛋白参与磁铁矿生物矿化机制的研究进展

生物矿化是生命体系中的一种重要而又特殊的生理过程。生命体中存在着各种各样的生物矿化产物,从生物体骨骼与牙齿到纳米级的金属氧化物都是生物矿化的产物。生物矿化与普通矿化的最大不同就是其反应过程中有生物分子、生物代谢、细胞以及有机基质的参与。多种生物因素参与的矿化反应,不仅反应条件温和,而且反应产物具有更好的材料性能和生物兼容性,最为典型的是趋磁细菌可以通过生物矿化过程形成尺寸均一、单磁筹的生物膜包裹着的磁性纳米晶体——磁小体。本文主要介绍了趋磁细菌重要磁小体膜蛋白以及铁载体蛋白(铁蛋白)在磁铁矿生物矿化过程中的作用和功能,综述了该领域的最新研究概况。通过对趋磁细菌发生生物矿化过程的深入探讨可进一步揭示生物大分子调控无机矿物生长的分子机制,为仿生合成新型生物材料提供重要的理论依据。     

Evaluation of enantiomeric purity of selected amino acids in honey

Highly sensitive and accurate HPLC methods were used for the determination of total amounts of proline, leucine and phenylalanine and their enantiomeric ratios in a variety of different honey samples. Significant amounts of D -leucine and D -phenylalanine and relatively low concentrations of D -proline have been found in honeys of different botanical and geographical origins. It is suggested that the enantiomeric ratios of amino acids could be used to test for storage effects, age, and the quality of the processing of the honey. © 1994 Wiley-Liss, Inc.     

D型氨基酸氧化酶活性对于D-硝基精氨酸手性转化的影响

D-硝基精氨酸(D-NNA)可在大鼠体内发生手性转化生成其L型异构体,即L-NNA,后者可抑制一氧化氮合酶活性,减少一氧化氮生成,升高动脉血压.研究了D型氨基酸氧化酶(DAAO)在D-NNA手性转化中的作用及DAAO对不同(包括已报道在体内可发生手型转化的)D型氨基酸的选择活性.体内实验显示,DAAO的选择性抑制剂苯甲酸钠(400mg/kg)或肌酐(400mg/kg)均可在不同程度上抑制D-NNA升压作用,进一步研究发现,肾脏或肝脏DAAO酶液在外加DAAO后可提高D-NNA的手性转化约2倍,表明DAAO对于D-NNA在体内的手性转化是必需的.DAAO酶液对可在体内发生手性转化且转化率相似(30%～50%)的D型氨基酸(D-Phe,D-Leu和D-NNA)的选择性表现出显著差异(Kcat/Km相差可达约15倍左右),这从另一方面表明体内D-硝基精氨酸氧化是其发生手性转化的前提条件但非决定因素.     

A Periplasmic Polymer Curves Vibrio cholerae and Promotes Pathogenesis

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Synthesis and characterisation of D-amino acid-based oligopeptides for use as probes of the influence of molecular structure on the paracellular route of gastrointestinal drug uptake

Summary A series of peptides based on D-amino-acids, and with an N-terminal D-phenylalanine residue, was synthesised by solution methods using t-butoxycarbonyl amino protection. These peptides were designed to resist metabolism in the gastrointestinal tract and to serve as probes of the effects of molecular shape and charge on the paracellular route of drug uptake in the gut. The peptides were characterised by NMR spectroscopy, FAB mass spectrometry, optical rotation and purified by HPLC.Abbreviations HBTU o-Benzotriazolyl-tetramethyluronium hexafluorophosphate - OSu N-hydroxysuccinimide ester     

Evaluation of free D-glutamate in processed foods

Monosodium glutamate (MSG) is added to many processed foods at significant levels for flavor enhancement. It is also naturally occurring at high levels in some foods. The enantiomeric composition of free glutamate in foods was examined and all foods analyzed were found to contain D -glutamate. The relative percent of D -glutamate in the food products studied depended on the origin of the glutamate. Foods to which MSG was added by the manufacturer had a high total level of MSG but a lower relative percentage of the D -enantiomer (usually less than 0.8%). In comparison, fermented foods tend to have high relative levels of D -glutamate but a lower total amount of the amino acid. The relative percent of D -glutamate in nonfermented foods containing no added MSG was also found to be low compared to fermented products. In some cases the percent D -glutamate could be related to the relative amounts of other food ingredients such as cheese. © 1994 Wiley-Liss, Inc.     

Simple and rapid screening method for microbial D-stereospecific peptidase and esterase

The use of a turbid plate containing Z-D-Ala-D-AlaOBzl was a convenient method for the screening of microorganisms with D-stereospecific peptidase activity as well as D-stereospecific esterase activity. This paper discusses the suitability of the developed method and its application to molecular cloning of D-stereospecifc peptidase and esterase genes.     

The ubiquitous cofactor NADH protects against substrate-induced inhibition of a pyridoxal enzyme.

In the usual reaction catalyzed by D-amino acid transaminase, cleavage of the alpha-H bond is followed by the reversible transfer of the alpha-NH2 to a keto acid cosubstrate in a two-step reaction mediated by the two vitamin B6 forms pyridoxal 5'-phosphate (PLP) and pyridoxamine 5'-phosphate (PMP). We report here a reaction not on the main pathway, i.e., beta-decarboxylation of D-aspartate to D-alanine, which occurs at 0.01% the rate of the major transaminase reaction. In this reaction, beta-C-C bond cleavage of the single substrate D-aspartate occurs rather than the usual alpha-bond cleavage in the transaminase reaction. The D-alanine produced from D-aspartate slowly inhibits both transaminase and decarboxylase activities, but NADH or NADPH instantaneously prevent D-aspartate turnover and D-alanine formation, thereby protecting the enzyme against inhibition. NADH has no effect on the enzyme spectrum itself in the absence of substrates, but it acts on the enzyme.D-aspartate complex with an apparent dissociation constant of 16 microM. Equivalent concentrations of NAD or thiols have no such effect. The suppression of beta-decarboxylase activity by NADH occurs concomitant with a reduction in the 415-nm absorbance due to the PLP form of the enzyme and an increase at 330 nm due to the PMP form of the enzyme. alpha-Ketoglutarate reverses the spectral changes caused by NADH and regenerates the active PLP form of the enzyme from the PMP form with an equilibrium constant of 10 microM. In addition to its known role in shuttling electrons in oxidation-reduction reactions, the niacin derivative NADH may also function by preventing aberrant damaging reactions for some enzyme-substrate intermediates. The D-aspartate-induced effect of NADH may indicate a slow transition between protein conformational studies if the reaction catalyzed is also slow.     

Chirality of amino acids of microorganisms used in food biotechnology

Bacteria of the genera Acetobacter, Bifidobacterium, Brevibacterium, Lactobacillus, Micrococcus, Propionibacterium, and Streptococcus, which are used as so-called starter cultures for the large-scale production of fermented foods and beverages in food biotechnology, have been investigated for the chirality of their amino acids (AA) by gas chromatography (GC). Bacteria were grown in complex media, centrifuged, and washed with 0.85% aqueous NaCl. Aliquots were totally hydrolyzed (6 M HCl, 110°C, 18 h), or extracted with 70% aqueous ethanol in order to isolated free AA. The AA were adsorbed on Dowex WX 8 cation-exchanger, eluted with 4 M ammonia and converted into their N(O)-trifluoroacetyl(TFA) 2-propyl esters or TFA methyl esters. The AA derivatives were investigated by capillary GC using the chiral stationary phases Chirasil-L -Val, Chirasil-D -Val, and Lipodex E. Besides L -AA, in all bacteria D -amino acids (D -AA) were detected; those in the highest relative amounts were D -Ala and D -Asp (occurring in all bacteria) and, in several cases, D -Glu. Lower, but significant amounts of other D -AA such as D -Ser, D -Pro, D -Val, D -Thr, D -Ile, D -Leu, D -Met, D -Phe, D -Tyr, D -Orn, and D -Lys were also detected in certain bacteria. These findings explain the origin of D -AA found in all fermented foods and drinks produced with the aid of bacterial starter cultures. © 1993 Wiley-Liss, Inc.     

Thiyl radicals and induction of protein degradation

Thiyl radicals are important intermediates in the redox biology and chemistry of thiols. These radicals can react via hydrogen transfer with various C-H bonds in peptides and proteins, leading to the generation of carbon-centered radicals, and, potentially, to irreversible protein damage. This review summarizes quantitative information on reaction kinetics and product formation, and discusses the significance of these reactions for protein degradation induced by thiyl radical formation.