Sensitivity of the Folding Pathway to the Details of Amino Acid Sequence

Experimental data on the structure of the transition state demonstrate that proteins with the same topology as a rule have similar folding nuclei (the structured formed part of the transition state). In this review discussed are the experimental works showing that the position of folding nuclei is different among proteins with the same topology. These facts emphasize that the folding pathway is sensitive to the details of amino acid sequence.     

Cysteine Sulfinic Acid in the Central Nervous System: Uptake and Release of Cysteine Sulfinic Acid by a Rat Brain Preparation

Abstract: Uptake and release of cysteine sulfinic acid by synaptosomal fractions (P₂) and slices of rat cerebral cortex were investigated. The P₂ fraction had a Na⁺-dependent high-affinity uptake system for cysteine sulfinic acid (K_m, 12μM), which was restricted to the synaptosomes. High-affinity uptake of cysteine sulfinic acid was competitively inhibited by glutamate, aspartate, and cysteic acid. None of the various centrally acting drugs tested specifically inhibited this transport system. Release of [¹⁴C]cysteine sulfinic acid from preloaded cortical slices or P₂ fractions was examined by a superfusion method, which avoided reuptake of released [¹⁴C]cysteine sulfinic acid. High K⁺ (56 m M ) and veratridine (10μM) stimulated the release of cysteine sulfinic acid from slices and the P₂ fraction in a partly Ca²⁺-dependent manner. Diazepam at concentrations of 10 and 100 μM markedly inhibited the stimulated release, but not the spontaneous release, by cortical slices. On the contrary, it had no effect on the stimulated release of cysteine sulfinic acid from the P₂ fraction.     

Application of the S-Pyridylethylation Reaction to the Elucidation of the Structures and Functions of Proteins

Cysteine (Cys) and cystine residues in proteins are unstable under conditions used for acid hydrolysis of peptide bonds. To overcome this problem, we proposed the use of the S-pyridylethylation reaction to stabilize Cys residues as pyridylethyl-cysteine (PEC) protein derivatives. This suggestion was based on our observation that two synthetic derivatives formed by pyridylethylation of the SH group of Cys with either 2-vinylpyridine (2-VP) or 4-vinylpyridine (4-VP), designated as S--(2-pyridylethyl)-L-cysteine (2-PEC) and S--(4-pyridylethyl)-L-cysteine (4-PEC), were stable under acid conditions used to hydrolyze proteins. This was also the case for protein-bound PEC groups. Since their discovery over 30 years ago, pyridylethylation reactions have been widely modified and automated for the analysis of many structurally different proteins at levels as low as 20 picomoles, to determine the primary structures of proteins and to define the influence of SH groups and disulfide bonds on the structures and functional, enzymatic, medical, nutritional, pharmacological, and toxic properties of proteins isolated from plant, microbial, marine, animal, and human sources. Pyridylethylation has been accepted as the best method for the modification of Cys residues in proteins for subsequent analysis and sequence determination. The reaction has also been proposed to measure D-Cys, homocysteine, glutathione, tryptophan, dehydroalanine, and furanthiol food flavors. This integrated overview of the diverse literature on these reactions emphasizes general concepts. It is intended to serve as a resource and guide for further progress based on the reported application of pyridylethylation reactions to more than 150 proteins.     

Cysteine Sulfinic Acid in the Central Nervous System: Specific Binding of [35S]Cysteic Acid to Cortical Synaptic Membranes-An Investigation of Possible Binding Sites for Cysteine Sulfinic Acid

Abstract: Specific binding sites for cysteine sulfinic acid, an excitatory amino acid, in crude synaptic membrane fractions of rat cerebral cortex were examined, using L-[³⁵S]cysteic acid as a ligand. Two specific binding systems of [³⁵S] cystec acid were found, one Na⁺-dependent and the other Na⁺-independent. The Na⁺-independent specific binding of [³⁵S]Cysteic acid was saturable, with a K_d of 474 n M and B_max of 3.29 pmol/mg protein. The binding was optimal at pH 7.4 and at 37°C. Treatment of the membranes with proteases, concanavalin A, or Triton X-100 markedly reduced the binding. Of various compounds related to cysteic acid, L-cysteine sulfinic acid was the most effective competitor of this binding. These results indicate the existence of an Na⁺-independent specific binding site for cysteic acid in the synaptic membrane of rat cerebral cortex, which may be different from that for glutamate. Possible involvement of cysteine sulfinic acid as an endogenous ligand for this binding site is discussed.     

微生物传感器及其在氨基酸分析中的应用

介绍了微生物传感器的发展状况、制作方法,综述了微生物传感器在氨基酸分析中的应用,引文献４２篇。     

氨基酸分析仪测定饲料添加剂——叶酸的方法

用６ｍｏｌ／Ｌ盐酸于１１０℃条件下水解饲料添加剂——叶酸,使之游离出谷氨酸,用氢氧化钠中和调节ｐＨ到２,氨基酸分析仪测定谷氨酸含量,经与标准叶酸水解样品比较,计算出叶酸的纯度。该方法重现性好,变异系数ＣＶ＝０．０８％,平均回收率为９８．３４％,浓度与峰面积呈线性相关,相关系数ｒ＝０．９９８７,可随氨基酸分析同时进行,不需改变任何分析条件。     

吊瓜籽中氨基酸质量分数的测定

样品吊瓜籽经酸水解处理,应用氨基酸分析仪进行分析,结果表明,吊瓜籽含所有常规17种氨基酸,质量分数高达23.28%,其中谷氨酸(G lu)和精氨酸(Agr)质量分数达4.39%和3.88%。     

人胃癌组织及胃正常组织氨基酸差异研究

对 2 2例胃癌组织及其癌边组织、胃正常组织氨基酸进行了测定。发现胃癌组织氨基酸总量低于癌边组织氨基酸总量 ,癌边组织氨基酸总量又低于胃正常组织氨基酸总量。癌中组织与癌边组织相比有 8种氨基酸明显降低 ,P <0 .0 1 ;其中三种为人体必需氨基酸 ,三种为生糖氨基酸。胃癌组织与胃正常组织相比 3种生糖氨基酸明显降低 ,P<0 .0 5。结果表明 :胃癌组织存在明显的氨基酸代谢异常     

用高效液相色谱定量分析分支链氨基酸

目的：周2,4-二硝基氟苯（DNFB）对分支链氨基酸衍生后,采用优化的高效液相色谱（HPLC）对其进行定量分析。方法：色谱柱为AgilentZORBAXEclipsAAA（4．6mm×150mm,5-Micron）,流动相为乙酸盐缓冲液（pH6．4）-乙腈,流速1．0mL／min,检测波长360nm。结果：用HPLC法测定分支链氨基酸的浓度为20-200mg／L时线性关系良好,3种分支链氨基酸的R。均在0．9997以上,平均回收率高,RSD≤0．56％（n=6）。结论：此方法快速、准确、重现性好,适合于对发酵液中分支链氨基酸的定量分析。     

氨基酸为显色剂比色法测定京尼平的含量

建立了一种京尼平含量的快速测定方法。研究了京尼平与氨基酸的显色反应条件,京尼平(0.0768mg·mL1)与氨基酸溶液(0.2mg·mL1)体积比为1:1,100℃下显色反应10min,检测波长590nm。该方法检测线性范围为0.76～30.73·g·mL1,线性回归方程为Y=0.2409X 0.0036,相关系数为0.9998,最低检测限为0.38μg·mL1,精密度为1.6%。本方法操作简便、快速,且结果准确可靠。     

Cysteine Sulfinic Acid in the Central Nervous System: Antagonistic Effect of Taurine on Cysteine Sulfinic Acid-Stimulated Formation of Cyclic AMP in Guinea Pig Hippocampal Slices

The stimulatory effect of cysteine sulfinic acid on cyclic AMP formation was examined in slices from three different regions of guinea pig brain. The inhibitory effect of taurine on the stimulated formation of cyclic AMP was also studied. Cysteine sulfinic acid (1--10 mM) greatly increased the cyclic AMP level in striatal, cortical, and especially hippocampal slices. In hippocampal slices, taurine (0.1--30 mM) markedly lowered the increase of cyclic AMP induced by cysteine sulfinic acid, but not that induced by glutamate or aspartate. In this region, taurine also reduced the stimulatory effects on cyclic AMP formation of adenosine, norepinephrine, and histamine, but not of depolarizing agents. It did not, however, inhibit the effects of any of these stimulants in cortical slices. These results suggest that sulfur-containing amino acids, such as cysteine sulfinic acid and taurine, regulate the cyclic AMP level in the hippocampus.     

不同产区太子参氨基酸含量测定及多元统计分析

本文采用高速氨基酸自动分析仪对太子参四大种植主产区(安徽、江苏、福建、贵州)的栽培品及河南的野生品,共13个批次太子参药材的氨基酸组成和含量进行测定。结果显示氨基酸含量基本顺序为:精氨酸(Arg)>谷氨酸(Glu)>天冬氨酸(Asp)>脯氨酸(Pro),其中安徽宣城产太子参样品(S2)的16种氨基酸总含量和7种人体必需氨基酸含量最高。以上述4种主要氨基酸作为指标,探讨了不同产区太子参药材的内在品质。采用聚类分析法对氨基酸含量进行多元统计分析,表明氨基酸含量分析可体现样品产区间和产区内的差异性,可区别野生品与栽培品。这些结果为发展太子参道地药材的质量标准控制提供了依据。     

诺丽果与热带水果中氨基酸含量及组成对比分析

以诺丽果和16种海南常见热带水果为材料,对比分析了氨基酸含量及组成。结果表明:诺丽果含有18种氨基酸,种类齐全。其氨基酸总量、人体必需氨基酸含量和儿童必需氨基酸含量均居第1位。诺丽果的E/T值为37.13%,E/N值为0.59,符合理想蛋白质的要求。诺丽果中各种人体必需氨基酸,Val、Ile、Leu、Phe+Tyr、M et+Cys、Thr的含量占氨基酸总量的比例,与1973年FAO/WHO修订的人体必需氨基酸含量模式谱基本一致,仅Lys中度缺乏。诺丽果中鲜味类、芳香族、甜味类氨基酸含量居第1位。     

小鼠海帕西啶1和2的氨基酸对比分析

海帕西啶是一种含有25个氨基酸的多肽类激素,在铁代谢过程中处于重要的地位。通过比对小鼠海帕西啶1和2发现,8位的异亮氨酸和25位的苏氨酸在哺乳动物中高度保守,因此认为这两种氨基酸可能对于海帕西啶的铁代谢功能发挥着重要的作用。     

毛细管电泳在氨基酸分析检测中的应用进展

对毛细管电泳技术的主要原理及其在氨基酸分析检测中的应用作了综述     

高效液相色谱测定蕨类植物中氨基酸含量

以5种蕨类植物(大羽贯众、美丽复叶耳蕨、黄山鳞毛蕨、狗脊蕨和紫萁)根状茎为研究材料,利用邻苯二甲醛柱前衍生高效液相色谱法分析了材料中的氨基酸成分.鉴于材料中蛋白质含量较低,测定方法中增加了样品的使用量并采用了梯度洗脱程序.结果表明,测试的5种蕨类植物所含总氨基酸含量较低,很少有超过5%,尤其在狗脊蕨中只有1.74%.在...     

芦笋茎叶游离氨基酸的提取及含量测定

通过对芦笋茎叶游离氨基酸提取工艺中温度、提取时间、料液比、乙酸浓度等影响因素的试验分析,确定芦笋茎叶游离氨基酸测定过程中的最佳提取条件为：提取温度60℃;料液比为1：35;提取时间为2．5h;并对芦笋茎叶游离氨基酸含量进行了测定,确定芦笋茎叶游离氨基酸含量为76．54mg／100g。     

氨基酸分析法快速测定梭曼中毒后大鼠脑组织中兴奋性氨基酸的含量

建立一种快速、准确、可靠的脑内兴奋性氨基酸定量检测方法 ,并观察梭曼惊厥后大鼠脑组织中兴奋性氨基酸(EAAs)含量变化。采用 6 30 0黄金系统氨基酸分析仪 ,在锂柱 130min程序生理体液分析方法基础上 ,根据兴奋性氨基酸(EAAs)的特性 ,建立了EAAs的快速测定方法 ,并用此方法对梭曼惊厥后不同时相大鼠的新鲜脑组织进行定位检测。梭曼诱发惊厥后大脑皮质和海马内谷氨酸和天冬门氨酸水平显著下降。惊厥 30min时谷氨酸下降最明显 ,分别是正常组的 5 3.2 %和 5 2 .8%。天门冬氨酸更易受梭曼中毒的影响 ,惊厥后 5、30、90min 3个时相点测定值均显著下降。此方法完成谷氨酸和天门冬氨酸分析的时间是 2 0min ,比原方法缩短了 110min ;且有较好的重现性 (GluCV :日内 1.86 % ,日间 2 .32 % ;AspCV :日内 1.42 ,日间 2 .48% )和回收率 (Glu 97.7% ;Asp97.3% )。兴奋性氨基酸参与了梭曼中毒性惊厥的病理生理过程。本方法定量检测兴奋性氨基酸快速、准确 ,并利于大批量样品的快速测定     

高纬度地区大豆蛋白含量及氨基酸组分的表型鉴定与聚类分析

对国内外高纬度地区的240份大豆种质资源的蛋白及16个氨基酸组分进行测定,通过遗传多样性、因子和聚类分析,进行了表型鉴定及基因型分类。结果表明,供试大豆种质蛋白及氨基酸组分变异较丰富,遗传多样性程度较高。根据因子分析,将筛选到的3个公因子进行聚类分析,可将供试种质资源分为7类。蛋白含量从高到低的顺序为类群Ⅶ>类群Ⅵ>类群Ⅴ>类群Ⅱ>类群Ⅰ>类群Ⅲ>类群Ⅳ。12个氨基酸组分的变化趋势与蛋白一致。类群Ⅶ和类群Ⅵ为高蛋白遗传群体,可作为高蛋白基因聚合育种的亲本材料。通过前期分析,筛选到24份高蛋氨酸资源,包括有公野04L-141、龙品03-311、Proto、和龙油太、猫眼豆、茶色豆、紫花2号、东农48等,可为高蛋氨酸种质创新提供材料基础。     

用有限酶切法分析蛋白质的氨基酸序列

报道了一个通过有限酶切蛋白质产生多肽片段的方法.蛋白质经单向SDS-聚丙烯酰胺凝胶电泳(SDS-PAGE)分离和用考马斯亮蓝短暂染色后,切下所需的蛋白质带,将其放入另一个SDS-PAGE凝胶的样品槽内,在电泳过程中该蛋白质被蛋白酶如蛋白酶V8降解,所产生的多肽片段随之被分离.电泳结束后,将多肽片段电印迹至聚偏二氟乙烯(polyvinylidene difluoride,PVDF)膜上.这些多肽片段从PVDF膜上切下后可以直接被用于分析氨基酸序列.该方法能广泛适用于分析一般蛋白质和N端被修饰蛋白质的氨基酸序列.