近红外光谱法测定5-羟基色氨酸的含量

本文利用近红外光谱法建立了5-羟基色氨酸的偏最小二乘(PLS)定量模型。采用相关数法选择波段以及二阶导数、Norris derivative平滑滤波进行数据预处理,所建校正模型的R为0.99907,RMSEC为0.0638,RMSEP为0.0675。经验证模型的预测性能良好,为5-HTP的快速测定提供了一种方法。     

Fluorescence Quantum Yields of Tryptophan and Tyrosine

Abstract

Fluorescence quantum yields (Q) for tyrosine, tryptophan, and phenylalanine in water at 23° determined by the comparative method using a quinine standard were found to be 0.14, 0.13, and 0.024, respectively. Similar values were obtained with phenol as the standard. The numbers are much lower than those literature values which have been widely used to calculate protein fluorescence quantum yields. Possible reasons for the discrepancies are discussed. The quantum yields of isomeric tyrosines and fluorophenylalanines are also reported.     

Identification of isomeric 5‐hydroxytryptophan‐ and oxindolylalanine‐containing peptides by mass spectrometry

Cells continuously produce reactive oxidative species that can modify all cellular components. In proteins, for example, cysteine, methionine, tryptophan (Trp), and tyrosine residues are particularly prone to oxidation. Here, we report two new approaches to distinguish two isomeric oxidation products of Trp residues, i.e. 5‐hydroxytryptophan (5‐HTP) and oxindolylalanine (Oia) residues, in peptides. First, 2‐nitrobenzenesulfenyl chloride, known to derivatize Trp residues in position 2 of the indole ring, was used to label 5‐HTP residues. The mass shift of 152.98 m/z units allowed identifying 5‐HTP‐ besides Trp‐containing peptides by mass spectrometry, whereas Oia residues were not labeled. Second, fragmentation of the Oia‐ and 5‐HTP‐derived immonium ions at m/z 175.08 produced ions characteristic for each residue that allowed their identification even in the presence of y₁ ions at m/z 175.12 derived from peptides with C‐terminal arginine residues. The pseudo MS³ spectra acquired on a quadrupole time‐of‐flight hybrid mass spectrometer displayed two signals at m/z 130.05 and m/z 132.05 characteristic for Oia‐containing peptides and a group of six signals (m/z 103.04, 120.04, 130.04, 133.03, 146.04, and 148.04) for 5‐HTP‐cointaining peptides. In both cases, the relative signal intensities appeared to be independent of the sequence providing a specific fingerprint of each oxidative modification. Copyright © 2012 John Wiley & Sons, Ltd.     

脯氨酸Ni(Ⅱ)修饰电极的制备及对甲醇氧化的催化(英文)

研究了聚色氨酸修饰玻碳电极（Ｐｏｌｙ－Ｔｒｙ／ＧＣ）的制备,用循环伏安法探讨了膜的电化学性质。在ｐＨ＝６．６的ＰＢＳ中,膜的循环伏安图上有两对氧化还原峰。掺杂金属离子Ｎｉ（Ⅱ）后的该聚合物膜修饰电极（Ｐｏｌｙ－Ｎｉ（Ⅱ） Ｔｒｙ／ＧＣ）对甲醇的催化活性大大提高,在０．０１ ｍｏｌ／Ｌ ＮａＯＨ中甲醇的氧化峰电位在０．６５ Ｖ,而同样条件下在空白玻璃电极（ＧＣ）和Ｐｏｌｙ－Ｔｒｙ／ＧＣ上甲醇的氧化峰电位要正得多。在０．１５ ｍｏｌ／Ｌ甲醇溶液中循环伏安扫描１５０ ｍｉｎ后,峰电流密度由１０６０ μＡ／ｃｍ～２降低至８８５μＡ／ｃｍ～２,然后峰电流密度不再降低,说明在电催化氧化甲醇过程中电极稳定性良好。     

Oxygen fluorescence quenching studies with single tryptophan-containing proteins

The work of Lakowicz and Weber [Biochemistry 12, 4161 (1973)] demonstrated that molecular oxygen is a powerful quencher of tryptophan fluorescence in proteins. Here we report studies of the oxygen quenching of several proteins that have a single, internal tryptophan residue. Among these are apoazurin (Pseudomonas aeruginosa), asparaginase (Escherichia coli), ribonuclease T₁ (Aspergillus oryzae), and cod parvalbumin. Both fluorescence intensity and phase lifetime quenching data are reported. By comparison of these data we find that there is a significant degree of apparent static quenching in these proteins. The dynamic quenching rate constants,k _q, that we find are low compared to those for tryptophan residues in other proteins. For example, for apoazurin we find an apparentk _q of 0.59×10⁹ M ^–1 s^–1 at 25°C. This value is the lowest that has been reported for the oxygen quenching of tryptophan fluorescence.     

Parametric models to compute tryptophan fluorescence wavelengths from classical protein simulations

Fluorescence spectroscopy is an important method to study protein conformational dynamics and solvation structures. Tryptophan (Trp) residues are the most important and practical intrinsic probes for protein fluorescence due to the variability of their fluorescence wavelengths: Trp residues emit in wavelengths ranging from 308 to 360 nm depending on the local molecular environment. Fluorescence involves electronic transitions, thus its computational modeling is a challenging task. We show that it is possible to predict the wavelength of emission of a Trp residue from classical molecular dynamics simulations by computing the solvent‐accessible surface area or the electrostatic interaction between the indole group and the rest of the system. Linear parametric models are obtained to predict the maximum emission wavelengths with standard errors of the order 5 nm. In a set of 19 proteins with emission wavelengths ranging from 308 to 352 nm, the best model predicts the maximum wavelength of emission with a standard error of 4.89 nm and a quadratic Pearson correlation coefficient of 0.81. These models can be used for the interpretation of fluorescence spectra of proteins with multiple Trp residues, or for which local Trp environmental variability exists and can be probed by classical molecular dynamics simulations. © 2018 Wiley Periodicals, Inc.     

基于氨基酸的Cu(Ⅱ)-色氨酸MOF催化剂上环氧化物与CO2环加成反应

由天然的/生物单元(氨基酸)构成的金属有机框架材料(MOFs)具有自然属性和丰富的酸/碱位和官能团,因而可用于CO2化学中.本文报道了氨基酸系含铜MOF(CuTrp,Trp = L-色氨酸)的催化效率.以甲醇为溶剂,在室温采用直接混合法合成了CuTrp催化剂,该方法具有很高的能量效率.采用X射线衍射、红外光谱、热重分析、电感耦合等离子体发射光谱法、扫描电镜和BET分析等手段对该催化剂进行了表征.采用环氧化物与CO2环加成制备环状碳酸酯反应评价了CuTrp催化剂活性.结果表明,在无溶剂条件下,CuTrp 催化剂可与四丁基溴化铵助催化剂发生协同作用.通过条件实验确定了优化的反应条件,并基于该实验结果和前期的密度泛函理论计算结果提出了反应机理.另外,CuTrp 催化剂在水中也表现出令人满意的稳定性,可重复使用三次以上而活性无明显下降.     

Total Synthesis of Keramamides A and L from a Common Precursor by Late‐Stage Indole Synthesis and Configurational Revision

The marine natural products keramamide A and L, members of the class of anabaenopeptin‐type peptides, were synthesized for the first time by a convergent and flexible route. The installation of the substituted tryptophan moieties was accomplished at the very end of the synthesis on the cyclic peptides, and thus enabled the synthesis of both natural products from one common precursor. The preparation of several epimers clearly indicates that the originally proposed relative configurations of both Keramamides A and L were not correct.     

Papain-induced Oligomerization of α-Amino Acid Esters

Oligomers of leucine, methionine, phenylalanine, and tyrosine were prepared enzymatically (using papain) from the respective methyl esters, with yields ranging from 51–96%. The effect of pH, buffer and salt concentration, and addition of alcohol on the oligomerization of leucine methyl ester was examined. The limits and potentialities of the enzymatic reaction as a method for obtaining monodisperse oligomers are discussed.     

Chemical Modification of Tryptophan Residues in Pullulanase

Tryptophan（Trp）residues in pullulanase have been chemically modified with N-bromossuccinimide（NBS）. The results of ultraviolet spectra indicated that there are 18 Trp residues in pullulanase and nine of them are located on the surface of the enzyme. Three of these Trp residues are none-essential residues which showed the fastest reaction speed by Zhou＇s plot. Two of the seven relative faster reacting residues are essential for the activity of the enzyme. The other eight are none-reactive residues with lowest reaction speed.