含硫氨基酸对猪生长性能及肠道功能的影响机制

含硫氨基酸包括甲硫氨酸(又名蛋氨酸)、胱氨酸和半胱氨酸,其中蛋氨酸是动物的含硫必需氨基酸,是猪必不可少的营养元素。研究表明,科学地添加含硫氨基酸对猪的摄食、生长、免疫等方面有着重要的作用。肠道是消化、吸收营养物质最主要的场所,含硫氨基酸的主要代谢产物谷胱甘肽可促进肠道屏障功能的恢复,牛磺酸能参与抗氧化反应、渗透调节等生理过程。因此,添加适量的含硫氨基酸有助于提高猪的生长性能,维持猪的肠道健康。     

束缚应激对大鼠同型半胱氨酸代谢的影响

为了探讨束缚应激对大鼠血清含硫氨基酸代谢的影响,根据同型半胱氨酸(Hcy)水平,将32只雄性Wistar大鼠分为对照组(control)、束缚应激组(RS)、1%蛋氨酸组(1%Met)和1%蛋氨酸+束缚应激组(1%Met+RS)。采用高压液相色谱法检测血清中的Hcy、半胱氨酸(Cys)和还原型谷胱甘肽(GSH)含量,采用全自动氨基酸分析仪测定血清中蛋氨酸(Met)和牛磺酸(Tau)含量。结果显示,RS组大鼠血清Hcy、Cys和GSH含量随着束缚时间延长而降低,且较对照组和1%蛋氨酸组有显著性差异(p<0.05);RS组大鼠血清Met和Tau含量较对照组和1%蛋氨酸组则显著升高(p<0.05)。束缚应激可能降低血清抗氧化能力和总Hcy水平。     

不同蝉花产品蛋白质营养价值分析

采用国际通用的营养价值评价方法 FAO/WHO,对野生蝉花、蝉花液体发酵菌丝体、蝉花固体培养孢梗束和菌质的蛋白质的营养价值进行了全面评价。结果显示,其蛋白质含量分别为19.65%、25.30%、32.90%和16.17%。野生蝉花和蝉花液体发酵菌丝体的第一限制氨基酸是含硫氨基酸(蛋氨酸和半胱氨酸),蝉花孢梗束的第一限制氨基酸是异亮氨酸,蝉花菌质的第一限制氨基酸是赖氨酸。综合评价,蝉花孢梗束蛋白质的营养价值最高,蝉花菌质蛋白质的氨基酸平衡性较好。     

外源性蛋氨酸对鲤鱼离体消化率及酶解速度的影响

蛋氨酸属于含硫氨基酸,参与体内甲基转移、磷的代谢以及肾上腺素、胆碱和肌酸的合成,是鱼类饲料中典型的限制性氨基酸,大部分鱼类蛋氨酸的需要量为蛋白质的2%―3%。但是随着氨基酸平衡性最好的蛋白质原料—鱼粉价格大幅上涨,其他廉价蛋白源在饲料中大量使用,使得限制性氨基酸—蛋氨酸的缺乏更加严重。要使饲料蛋白质中的必需氨基酸组成趋于平衡,就要求我们能够有效的补充限制性氨基酸。现阶段,已经有越来越多的水产     

高同型半胱氨酸血症致动脉粥样硬化的细胞分子机制

同型半胱氨酸（homocysteine,Hcy)是蛋氨酸代谢途径产生的含硫氨基酸,其代谢紊乱可以诱导高同型半胱氨酸血症的发生,已被临床及流行病学资料证实为动脉粥样硬化发病的独立危险因子。Hcy通过激活二酰甘油－蛋白激酶C－（DAG－PKC）及丝裂素活化蛋白激酶（MAPK）途径,诱导相关基因的表达,促进细胞钙化,启动脂质过氧化应激,从而损伤心血管系统。金属硫蛋白,牛磺酸,L－精氨酸作为内源性小分子物质,成为继维生素B6,B12之后控制和治疗高同型半胱氨酸血症的新途径。     

DL-蛋按酸及衍生物的合成与拆分研究进展

综述了蛋氨基酸及其衍生物的化学合成及化学拆分近年来的研究进展.第一部分讨论了DL-蛋氨酸及其衍生物的化学合成,包括丙烯醛法、丙二酸酯法,氨基内酯法等,并着重介绍了海因法.第二部分为 DL-蛋氨酸的手性拆分,主要包括膜分离,加合物、络合物形式分离,用苯丙氨酸拆分,衍生物分离等拆分方法,还介绍了生物酶拆分方法和其它有关拆分方法的进展.     

不同叶菜型甘薯品种的氨基酸含量及组成分析

选用7个叶菜型甘薯品种,测定分析了茎尖中氨基酸含量及组成。结果表明:甘薯茎尖的E/T值变幅为37.22%~39.60%,E/N值变幅为0.59~0.66,符合理想蛋白质的要求;各种人体必需氨基酸占氨基酸总量的相对含量大部分符合1973年FAO/WHO修订的人体必需氨基酸模式谱,仅蛋氨酸+半胱氨酸中度缺乏;在全部18种氨基酸中,以半胱氨酸、蛋氨酸、色氨酸的变异系数最大,其他15种氨基酸的变异系数较小。     

大豆含硫氨基酸相关酶基因发掘

大豆(Glycine max)含硫氨基酸合成途径中的酶基因是含硫氨基酸组分的重要调控基因,发掘相关酶基因对高含硫氨基酸分子育种具有重要意义。文章采用大豆物理与遗传整合图谱,通过BioMercator2.1将113个含硫氨基酸合成途径酶基因及33个控制含硫氨基酸含量的QTL整合到遗传图谱Consensus Map 4.0上,依据酶基因位点与QTL的一致性以及QTL的效应值,初步筛选到16个与含硫氨基酸合成相关的候选基因。通过生物信息学方法对候选基因进行拷贝数、SNP、表达谱等分析,鉴定到12个相关酶基因,分别位于D1a、M、A2、K和G等8个连锁群上。生物信息学分析显示这些基因所在QTL可解释含硫氨基酸遗传变异的6.0%~38.5%,其中9个基因的间接效应值超过10%。12个相关酶基因参与含硫氨基酸代谢的重要途径,且多在子叶、花中高丰度表达,存在丰富的SNP。这些基因可作为候选基因进行功能标记开发,将为大豆分子设计育种奠定基础。     

10kD玉米醇溶蛋白基因的克隆与植物表达载体构建

由于紫花苜蓿中的含硫氨基酸水平很低,采用基因工程手段将富硫蛋白基因-10kD玉米醇溶蛋白(zein)基因转入苜蓿中以提高其水平。根据该基因的保守序列设计引物,并在下游引物终止密码子前引入内质网驻留蛋白信号序列(KDEL),通过PCR技术从玉米(Zea mays L.)黄化幼苗基因组中扩增目的基因的开放阅读框(ORF)。序列测序得到全长为465bp的目的片断,该片段编码154个氨基酸,其中甲硫氨酸(M)31个占20.13%,半胱氨酸(C)6个占3.90%,含硫氨基酸共占24.03%。该基因与报道的10kD玉米醇溶蛋基因具有很高的同源性。将该基因构建到植物表达载体pCAMBIA13011上,以转化紫花苜蓿提高其含硫氨基酸的水平。     

非转基因和转基因小麦中氨基酸含量的分析及比较

目的：对小麦中氨基酸分析的水解方法进行研究,比较非转基因和转基因小麦中氨基酸的含量。方法：样品用含0.1%巯基乙酸的盐酸溶液水解提取,样液经定容、过滤、浓缩、复溶、过膜后,用氨基酸分析仪测定,外标法定量。结果：应用含巯基乙酸的盐酸水解液对小麦样品进行水解的同时有效防止了含硫氨基酸（蛋氨酸和半胱氨酸）的氧化,相对氧化水解方法节省前处理时间,方法的回收率为93%~99%,相对标准偏差小于2.4%。非转基因和转基因小麦样品的17种氨基酸分析,氨基酸含量不存在显著性差异。结论：该方法准确快速、重现性好,适用于小麦中氨基酸含量分析的检测要求。     

Fluorescent labeling of cell-free synthesized proteins by incorporation of fluorophore-conjugated nonnatural amino acids

Although fluorescent dyes, such as fluorescein derivatives, have bulky and complex structures, nonnatural amino acids carrying these fluorescein derivatives are acceptable by the Escherichia coli ribosome and are useful for the cotranslational fluorescent labeling of cell-free synthesized proteins. Surprisingly, the incorporation efficiency of nonnatural amino acids carrying fluorescein derivatives into translated proteins depends on the source of the translational machinery used in cell-free protein synthesis. That is, whereas the E. coli ribosome efficiently supported the incorporation of nonnatural amino acids carrying fluorescein derivatives into a protein structure, no detectable fluorescent signal was observed from the protein expressed in the eukaryotic cell-free protein synthesis system performed in the presence of fluorescein-conjugated aminoacylated transfer RNA (tRNA).     

Capillary electrochromatographic study of the interactions of porphyrin derivatives with amino acids and oligopeptides

Open-tubular capillary electrochromatography (OT-CEC) was used to study the interactions of synthetic (metallo)porphyrin derivatives (immobilized by physical adsorption to the fused-silica capillary wall) with three aromatic amino acids (phenylalanine, tyrosine, tryptophan), three aliphatic amino acids (beta-alanine, proline, valine) and two oligopeptides (diglycine, triglycine). The effective mobilities of amino acids and peptides measured in OT-CEC mode in the acid and alkaline background electrolytes (BGEs) were compared with those obtained by capillary zone electrophoresis (CZE) in the bare fused-silica capillary in the same BGEs. In this way the influence of the peripheral substituents and the character of the central metal atom in porphyrin derivatives on the interactions with amino acids and peptides in the acid and alkaline media was investigated. Three types of noncovalent interactions, axial ligation to the central metal atom, pi-pi stacking and electrostatic repulsion seem to take part in the interactions of analyzed amino acids and peptides with porphyrin derivatives, resulting in a better separation of these analytes by OT-CEC than by CZE.     

Substrate specificity of the amino acid transporter PAT1

Summary. The proton coupled amino acid transporter PAT1 expressed in intestine, brain, and other organs accepts L- and D-proline, glycine, and L-alanine but also pharmaceutically active amino acid derivatives such as 3-amino-1-propanesulfonic acid, L-azetidine-2-carboxylic acid, and cis-4-hydroxy-D-proline as substrates. We systematically analyzed the structural requirements for PAT1 substrates by testing 87 amino acids, proline homologs, indoles, and derivatives. Affinity data and effects on membrane potential were determined using Caco-2 cells. For aliphatic amino acids, a blocked carboxyl group, the distance between amino and carboxyl group, and the position of the hydroxyl group are affinity limiting factors. Methylation of the amino group enhances substrate affinity. Hetero atoms in the proline template are well tolerated. Aromatic α-amino acids display low affinity. PAT1 interacts strongly with heterocyclic aromatic acids containing an indole scaffold. The structural requirements of PAT1 substrates elucidated in this study will be useful for the development of prodrugs.     

A biomimetic domino reaction for the concise synthesis of capreomycidine and epicapreomycidine

The non-proteinogenic amino acids capreomycidine and epicapreomycidine are constituents of antibiotically active natural products, but the synthesis of these unusual cyclic guanidine derivatives is challenging. The biosynthesis of capreomycidine has therefore been employed as a guideline to develop a concise biomimetic synthesis of both epimeric amino acids. The resulting domino-guanidinylation-aza-Michael-addition reaction provides the most convenient access to these amino acids in racemic form. Attempts to dissect the domino reaction into two separate transformations for a stereocontrolled version of this synthetic approach have also been made. The synthesized didehydro-arginine derivatives with urethane-protected guanidine moieties did not undergo the aza-Michael-addition anymore. These results may have wider implications for the 1,4-addition of guanidines to α,β-unsaturated carbonyl compounds, particularly to didehydro amino acids.     

Use of t-butyldimethylsilylation in the gas chromatographic/mass spectrometric analysis of physiologic compounds found in plasma using electron-impact ionization

The use of N-methyl-N-(t-butyldimethylsilyl)trifluoroacetamide to prepare the t-butyldimethylsilyl derivatives of a number of organic compounds (selected amino acids, alpha-keto acids, ketone bodies, free fatty acids, urea, glycerol, lactate, and pyruvate) is reported. These derivatives are particularly useful for gas chromatographic/mass spectrometric analysis involving the use of stable isotopes and selected ion monitoring, since a peak of sufficient abundance at 57 mass/charge units below the molecular ion was always present, and was the result of the loss of one t-butyl group. In each case, this fragment contained the entire skeleton of the original compound, which permitted easy analysis using electron-impact ionization of these compounds alone or when labeled with stable isotopes in any nonexchangeable position.     

A simple quantitative method for the determination of 3-fluorotyrosine substitution in proteins

A rapid quantitative method is described for determining 3-fluorotyrosine incorporation into proteins. Derivatives of tyrosine and 3-fluorotyrosine with o-phthalaldehyde are well separated from one another by a reverse-phase high-performance liquid chromatography system used for routine analyses of o-phthalaldehyde-amino acid derivatives. Since both amino acids are well resolved from all other derivatized amino acids, the method is useful for amino acid analyses of proteins. Determination of the fluorotyrosine content of proteins by this method involves a single separation step, is reproducible, and requires no corrections for stability or yield. Further, the o-phthalaldehyde derivatives of 5-fluorotryptophan, 2-fluorophenylalanine, 3-fluorophenylalanine, and 4-fluorophenylalanine can also be resolved. The method may be generally applicable to fluorinated aromatic amino acid-labeled proteins that are studied structurally and dynamically by nuclear magnetic resonance.     

T.l.c. enantiomeric separation of amino acids

Resolution of enantiomers is very important particularly in the fields of asymmetric synthesis, mechanistic studies, geochronology, studies of structure-function relationship of proteins, pharmacology, and medicine. Various chromatographic methods have replaced the classical fractional crystallization, seeding and enzymatic procedures. Of these, t.l.c. provides a direct, simple, and inexpensive method for resolution of enantiomers of amino acids and their derivatives. Ligand exchange, ion exchange, and molecular inclusion complexation have been the basis of t.l.c. resolution of enantiomers of amino acids and their derivatives. The innovation of new plate types, and methods of development and detection have renewed interest in the direct resolution of enantiomers of amino acids, their derivatives and a variety of other compounds by t.l.c. The present report provides an overview of some of the more recent approaches to the direct t.l.c. resolution of amino acids and their derivatives together with special advantages and scope of t.l.c.     

Nsc and Fmoc Nalpha-amino protection for solid-phase peptide synthesis: a parallel study.

The 2-(4-nitrophenylsulfonyl)ethoxycarbonyl (Nsc) group is an alternative to Fmoc for Nalpha-protection in solid-phase peptide synthesis. Nsc-amino acids may be particularly suitable for automatic synthesizers, in which the amino acids are stored in solution, and the incorporation of residues prone to racemization such as Cys and His. Owing to the hydrophilicity of the Nsc group, these derivatives are useful for the preparation of protected peptides in convergent solid-phase peptide synthesis strategies.     

A modified system for thiazolinone conversion to thiohydantoin derivatives and their separation by high-pressure liquid chromatography

An improved and very simple procedure for thiazolinone conversion to thiohydantoin derivatives and their separation by reverse-phase high-pressure liquid chromatography is described. Trifluoroacetic acid (10%) in ethyl acetate has been employed as a conversion reagent to circumvent the deamidation of acid amides and methylation of acidic amino acids, with a concomitant increase in the detection limits of these residues. Additionally, a very simple procedure has been developed for the separation of phenylthiohydantoin (PTH) derivatives of amino acids. The system takes advantage of the computer-controlled precise mixing of the solvents A and B to achieve accurate pH and thus avoid the necessity of pH adjustment of a buffer. The procedure is simple and highly reproducible, and separates all the 20 known PTH amino acids. The efficiency of the method has been examined on synthetic and natural proteins/peptides, in manual and autoconversion systems, over a period of more than 18 months.     

The stability of the o-phthalaldehyde/2-mercaptoethanol derivatives of amino acids: an investigation using high-pressure liquid chromatography with a precolumn derivatization technique

The investigation of the stabilities of o-phthalaldehyde/2-mercaptoethanol derivatives of amino acids using a precolumn reaction technique and a high-pressure liquid chromatographic procedure is reported. The amino acid derivatives are shown to be stable on the high-pressure liquid chromatography column. Optimal conditions for the development of these derivatives for their separation using this technique are recommended.