用日立L－8500氨基酸分析仪测定明胶中的蛋氨酸、蛋氨酸砜及蛋氨酸亚砜

明胶中微量的蛋氨酸（Ｍｅｔ）、蛋氨酸砜（ＭｅｔｓｏＮ）以及蛋氨酸亚砜（ＭｅｔｓｏＸ）的含量测定是研究感光材料的科研人员十分关心的问题,多年来没有一个较好的测定方法。本文介绍了利用Ｌ－８５００氨基酸分析仪在测定明胶中其他氨基酸的同时准确地测定Ｍｅｔ、ＭｅｔｓｏＮ及ＭｅｔｓｏＸ的含量,方法简便、快速、准确。     

羟基蛋氨酸及其钙盐的合成研究进展

羟基蛋氨酸钙是复方α-酮酸片中一个重要成分,可防止氨基酸缺乏和改善代谢紊乱,对肾功能衰竭具有一定的疗效,并对钙代谢和继发性甲状旁腺功能亢进都具有益作用,同时也是重要的有机合成、药物合成及生物合成中间体.本文对近年来羟基蛋氨酸及其钙盐的合成方法进行了综述.重点介绍了氰醇水解法、蛋氨酸转化法、酮酸转化法、酮醇氧化法、氰代磷酸二乙酯法和α-羟基-γ-丁内酯法等在羟基蛋氨酸及其钙盐合成中的应用.     

提高苜蓿中蛋氨酸含量的方法

苜蓿素有牧草之王的美称,也是一种天然的饲料,但其中必需氨基酸—蛋氨酸的含量极低,提高其蛋氨酸的含量对畜牧业有极大的经济价值。本文对近几年提高苜蓿中含硫氨基酸酸的含量的方法及其合成途径进行综述,以期为国内研究及生产单位提供参考。     

DL-蛋氨酸及其衍生物的合成与拆分研究进展

综述了蛋氨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     

DL-蛋氨酸及其衍生物的合成与拆分研究进展

综述了蛋氨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     

发酵法生产S-腺苷蛋氨酸前体蛋氨酸补加策略

利用酿酒酵母菌株高密度发酵法生产S-腺苷蛋氨酸关键的影响因素之一是前体L-蛋氨酸的补加策略.本研究采用一支经过常规诱变处理的S-腺苷蛋氨酸优势积累菌株酿酒酵母SAM0801,通过5 L发酵罐高密度发酵实验研究,考察了6种补加策略,最终确定了L-蛋氨酸的加入时机为30h左右,当茵体干重达到100g/L时,补加量为每罐40gL-蛋氨酸,发酵58 h左右达到最高生物量干重168 g/L,产量14.48 g/L.     

罗非鱼对晶体蛋氨酸、包膜蛋氨酸利用的比较研究

为比较罗非鱼对晶体蛋氨酸、包膜蛋氨酸的利用效果, 设计了鱼粉含量为9%的鱼粉饲料、鱼粉含量为0%的无鱼粉饲料(以豆粕等蛋白替代鱼粉), 在无鱼粉饲料基础上分别添加晶体蛋氨酸、包膜蛋氨酸, 使其蛋氨酸含量与鱼粉饲料一致, 共4种饲料, 饲喂平均体重为(1.220.07) g/尾的奥尼罗非鱼(Oreochromis niloticus O. aureus) 8周。结果表明, 各组罗非鱼增重率分别为1642.7%、1250.3%、1362.0%、1451.7%, 饲料系数分别为1.08、1.45、1.30、1.21; 在无鱼粉饲料中添加晶体蛋氨酸、包膜蛋氨酸提高增重率8.9%、16.1% (P0.05), 降低饲料系数10.34%、16.55% (P0.05); 包膜蛋氨酸组较晶体蛋氨酸组具有更高增重率和更低饲料系数(P0.05)。对摄食后不同时间点肝脏和血浆谷草转氨酶(GOT)、谷丙转氨酶(GPT)活性变化的测定表明, 鱼粉饲料组、无鱼粉饲料组肝脏GOT、GPT活性分别在摄食后第2、第4h出现高峰; 晶体蛋氨酸组在摄食后1h出现高峰, 较无鱼粉组提前; 包膜蛋氨酸组在摄食后第5h出现高峰, 较无鱼粉组滞后; 血浆GOT、GPT活性变化趋势与肝脏的基本一致。消化率试验表明, 鱼粉饲料组干物质、粗蛋白质消化率最高, 无鱼粉饲料组最低; 在无鱼粉饲料中添加晶体蛋氨酸、包膜蛋氨酸后, 干物质、粗蛋白质消化率均得到显著提高(P0.05)。上述结果表明, 在蛋氨酸缺乏的实用饲料中补充晶体或包膜蛋氨酸, 均可显著提高罗非鱼生长性能和营养物质消化率, 包膜蛋氨酸较晶体蛋氨酸具有更高的利用效率和更好的促生长效果。     

S-腺苷蛋氨酸研究进展

S-腺苷蛋氨酸(SAM)是生物体内重要的中间代谢物质,参与多种生化反应．重点介绍了 S-腺苷蛋氨酸的制备和稳定性研究,同时综述了其生理功能、提取纯化和分析检测及临床应用．     

甲硫氨酸诱导高Hcy血症的抗氧化作用研究

为探讨甲硫氨酸在诱导高Hcy血症过程中的抗氧化作用,将Wistar大鼠随机分为正常组和1%甲硫氨酸组,喂养6周后,采用高效液相色谱法测定血清中同型半胱氨酸(Hcy)和谷胱甘肽含量(GSH),全自动氨基酸分析仪测定蛋氨酸和牛磺酸含量,转氨酶活性采用试剂盒测定。肝组织丙二醛(MDA)含量采用硫代巴比妥酸法,黄嘌呤氧化酶法和比色法测定肝组织超氧化物歧化酶(SOD)活性、总抗氧化能力(FRAP值)和还原性谷胱甘肽含量。结果表明,1%甲硫氨酸组血清Hcy和牛磺酸含量分别为3.56±0.68μmol·L-1和568.68±57.02μmol·L-1,较正常组显著升高(p<0.05)。1%甲硫氨酸组肝组织GSH含量和SOD活性分别为132.19±25.49mg·g-1和6.86±1.46U·mg-1,较正常组103.97±16.30mg·g-1和5.01±1.24U·mg-1显著升高(p<0.05)。1%甲硫氨酸组较正常组肝组织FRAP值亦升高而MDA含量降低。结果表明,甲硫氨酸在诱导高Hcy血症过程中同时具有抗氧化作用。     

Methionine anchoring applied to the solid-phase synthesis of lysine-containing 'head-to-tail' cyclic peptides

Lysine-containing 'head-to-tail' cyclic peptides can be prepared via a side-chain anchoring solid-phase synthesis strategy. A handle is prepared using a methionine residue, the C -carboxylof which forms an amide with the N -amine of lysine. Subsequently, the linear peptide sequence is assembled, appropriatedeblocking steps are carried out, and on-resin head-to-tail cyclizationfollows. Optionally, acid-labile protecting groups may be removed while the peptide remains resin-bound. The final cleavage step uses CNBr, and releases the free or protected cyclic peptide into solution.     

Methionine catabolism in Saccharomyces cerevisiae

The catabolism of methionine to methionol and methanethiol in Saccharomyces cerevisiae was studied using (13)C NMR spectroscopy, GC-MS, enzyme assays and a number of mutants. Methionine is first transaminated to alpha-keto-gamma-(methylthio)butyrate. Methionol is formed by a decarboxylation reaction, which yields methional, followed by reduction. The decarboxylation is effected specifically by Ydr380wp. Methanethiol is formed from both methionine and alpha-keto-gamma-(methylthio)butyrate by a demethiolase activity. In all except one strain examined, demethiolase was induced by the presence of methionine in the growth medium. This pathway results in the production of alpha-ketobutyrate, a carbon skeleton, which can be re-utilized. Hence, methionine catabolism is more complex and economical than the other amino acid catabolic pathways in yeast, which use the Ehrlich pathway and result solely in the formation of a fusel alcohol.     

Methionine anchoring applied to the solid-phase synthesis of lysine-containing 'head-to-tail' cyclic peptides

Summary Lysine-containing ‘head-to-tail’ cyclic peptides can be prepared via a side-chain anchoring solid-phase synthesis strategy. A handle is prepared using a methionine residue, theC ^α-carboxyl of which forms an, amide with theN ^ε-amine of lysine. Subsequently, the linear peptide sequence is assembled, appropriate deblocking steps are carried out, and on-resin head-to-tail cyclization follows. Optionally, acid-labile protecting groups may be removed while the peptide remains resin-bound. The final cleavage step uses CNBr, and releases the free or protected cyclic peptide into solution. Taken in part from the Ph.D. Thesis of J. C. Kappel, University of Minnesota, November 2003. Portions of this work were reported in preliminary form at the Eighteenth American Peptide Symposium, Boston, MA, U.S.A., 19–23 July 2003, and at the Eighth International Symposium on Solid Phase Synthesis and Combinatorial Chemical Libraries, London, England, U.K., 2–5 September 2003.     

高蛋氨酸饮食对大鼠血管内皮细胞分泌功能的影响

目的:探讨高蛋氨酸饮食对大鼠血管内皮细胞分泌功能的影响。方法:雄性Wistar大鼠随机分为正常饮食对照组(对照组)和高蛋氨酸饮食组(高蛋氨酸组)。对照组喂饲普通饲料,高蛋氨酸组大鼠喂饲含3%蛋氨酸的饲料,共8周。采用高效液相色谱法测定大鼠血浆同型半胱氨酸含量,以MDA、SOD、NO/ET和t-PA/PAI平衡等指标建立研究平台和内皮功能评价体系,同时以扫描电镜观察主动脉弓血管内皮细胞形态。结果:与对照组相比,高蛋氨酸组血浆Hcy含量显著高于对照组,是对照组的2倍以上;血浆MDA和SOD活力显著升高(P<0.05),t-PA/PAI-1和NO/ET比值均显著降低(P<0.05)。扫描电镜显示高蛋氨酸组大鼠内皮细胞呈典型虫蛀样损害,伴有附壁血栓形成和脂质沉积。结论:高蛋氨酸饮食可诱发大鼠高半胱氨酸血症,Hcy可通过氧化应激机制损伤血管内细胞分泌功能,血浆NO/ET和t-PA/PAI-1系统失衡。     

Methionine oxidation and reduction in proteins

Background

Cysteine and methionine are the two sulfur containing amino acids in proteins. While the roles of protein-bound cysteinyl residues as endogenous antioxidants are well appreciated, those of methionine remain largely unexplored.

Scope

We summarize the key roles of methionine residues in proteins.

Major conclusion

Recent studies establish that cysteine and methionine have remarkably similar functions.

General significance

Both cysteine and methionine serve as important cellular antioxidants, stabilize the structure of proteins, and can act as regulatory switches through reversible oxidation and reduction. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.     

Methionine adenosyltransferase as a useful molecular systematics tool revealed by phylogenetic and structural analyses

Structural and phylogenetic relationships among Bacteria and Eukaryota were analyzed by examining 292 methionine adenosyltransferase (MAT) amino acid sequences with respect to the crystal structure of this enzyme established for Escherichia coli and rat liver. Approximately 30% of MAT residues were found to be identical in all species. Five highly conserved amino acid sequence blocks did not vary in the MAT family. We detected specific structural features that correlated with sequence signatures for several clades, allowing taxonomical identification by sequence analysis. In addition, the number of amino acid residues in the loop connecting beta-strands A2 and A3 served to clearly distinguish sequences between eukaryotes and eubacteria. The molecular phylogeny of MAT genes in eukaryotes can be explained in terms of functional diversification coupled to gene duplication or alternative splicing and adaptation through strong structural constraints. Sequence analyses and intron/exon junction positions among nematodes, arthropods and vertebrates support the traditional Coelomata hypothesis. In vertebrates, the liver MAT I isoenzyme has gradually adapted its sequence towards one providing a more specific liver function. MAT phylogeny also served to cluster the major bacterial groups, demonstrating the superior phylogenetic performance of this ubiquitous, housekeeping gene in reconstructing the evolutionary history of distant relatives.     

Inactivation of Bacillus stearothermophilus Leucine Aminopeptidase II by Hydrogen Peroxide and Site-Directed Mutagenesis of Methionine Residues on the Enzyme

Leucine aminopeptidases (LAPs) are exopeptidases that remove the N-terminal L-leucine from peptide substrates. Oxidative stability assay showed that the recombinant Bacillus stearothermophilus LAP II (rLAPII) was sensitive to oxidative damage by hydrogen peroxide at the elevated temperature. The H2O2-treated enzyme experienced obvious changes in the secondary structure when the oxidant concentration increased to 300 mM. To investigate the role of methionine residues on the oxidative inactivation, each of the five methionine residues in the rLAPII was replaced with leucine by site-directed mutagenesis. The mutant enzymes with an apparent Mr of approximately 44.5 kDa were overexpressed in Escherichia coli and were purified to homogeneity by nickel-chelate chromatography. The specific activities for Met82Leu, Met88Leu, Met254Leu, and Met382Leu were similar to that of the wild-type enzyme, whereas a reduced activity was observed in Met136Leu. The 50% decrease in the catalytic efficiency (kcat/Km) for Met136Leu was caused by 47% decrease in kcat value. As compared with the wild-type enzyme, all mutant proteins were more sensitive to the oxidant, implying that the methionine residues of B. stearothermophilus LAP II are important for the protection of the enzyme from oxidative inactivation.     

Methionine uptake of larval and adult Schistosoma mansoni;

The uptake of methyl-¹⁴C-methionine by schistosomula, 21 day-old and adult Schistosoma mansoni in vitro has been investigated. Ligation of the adult pharynx and comparison between the kinetics of uptake of schistosomula and adults suggests that methionine is absorbed, in the system described, primarily via the tegument. All stages of the parasite examined absorb methionine by, at least, two kinetically distinguishable systems, one which is saturable and a second which appears to be simple diffusion. The saturable system has relatively low specificity for amino acids but shows no affinity for other classes of compounds. The effects of pH, temperature, metabolic inhibitors, and sodium ion concentration have been examined. The results are discussed with reference to schistosome gut function and also to the differential response to chemotherapy according to age of infection.