磷酰化与非磷酰化蛋氨酸水溶液的脉冲辅解研究

•OH radical induced oxidation of methionine and N-phosphoryl methionine in aqueous solutions has been investigated using optical pulse radiolytical technique, the influence of N-phosphoryl group on the radiolytical processes of methionine has been explained by molecular structure and the rate constants of oxidation of N-phosphoryl methionine (NDM) by the •OH radicals at different pH values have been determined. This research result suggests that the phosphonate ester has a coordinating effect on the radioprotection of methionine to the biological systems.     

磷酰化肽链中电子转移的ESR研究

当前生命科学正以前所未有的速度向前发展，从对核酸的深入研究开始过渡到对蛋白质结构与功能的注意，尤其是近年来基因调控研究的重大进展是发现非组蛋白具有高度的磷酸化的特性［1］，研究证明，核内蛋白磷酸化和去磷酸化则是基因表达调控的重要方式之一［2，3］，它是酶活性调节、基因表达调控、细胞转化恶变的关键环节；同时在解决肿瘤的发生和治疗、病毒的感染和诊治、辐射损伤、抗衰老等实际问题上有突出意义，如1992年Krebus和Fisher因为在蛋白的可逆磷酸化方面的突出贡献而获得诺贝尔生理和医学奖．而电子转移是一切化学变化的基础…     

水溶液中磷酰化组氨酸与其它氨基酸的交叉成肽研究

水溶液中磷酰化组氨酸与其它氨基酸的交叉成肽研究沙耀武，赵玉芬（清华大学化学系，北京１０００８４）一些氨基酸在前生化时期的条件下，就可以由甲烷、氨和水通过高压放电生成［１，２］。如果向该反应体系中加入三氢化磷，生成的氨基酸的种类增多、结构的复杂性也提高...     

高氯酸铒与蛋氨酸配合物的合成及结构研究

在水溶液中合成了标题配合物，其化学式为Ｅｒ（Ｍｅｔ）２（ＣｌＯ４）３·４．５Ｈ２Ｏ（Ｍｅｔ为蛋氨酸）．研究了配合物的红外光谱．用Ｘ射线单晶衍射法测定了配合物的晶体结构，结果表明，其结构式为［Ｅｒ２（ＤＬ－Ｍｅｔ）４·８Ｈ２Ｏ］·（ＣｌＯ４）６·Ｈ２Ｏ．属单斜晶系，空间群为Ｐ２１／ｎ，晶胞参数为：ａ＝１３．８４６（５）Ａ，ｂ＝２１．７９４（７）Ａ，Ｃ＝１９．１３１（５），β＝９０．５１（３）°，Ｖ＝５７７２．８４（３）３，Ｚ＝４．每两个Ｅｒ原子之间通过四个蛋氨酸的羧基桥相连而形成双核配合物．两对对位的蛋氨酸中，其中一个为Ｌ型，而另一个为Ｄ型．每个Ｅｒ原子还与四个水分子配位，其配位数为８．对于每个双核离子而言，其配位多面体由两个四方反棱柱体组成．     

磷酰化剂的进展

只要提及光合作用、新陈代谢、糖的合成、核酸、磷脂以及磷所参与的辅酶,就可知道磷在生物体中占有极其重要的地位,而这一切都与磷酰化反应密切相关。磷酰化反应是指将磷酰基[(RO)_2P(O)—]从磷酰化剂转移至一个亲核中心以生成新的有机磷酸衍生物,而凡能以游离形式(R=H)或酯化形式(R=烃基)将磷酰基进行转移的化合物均可称作磷酰化剂。     

二乙氧基磷酰化香豆素的合成与表征

在生命过程中磷酰化和去磷酰化起着重要作用。一些生物分子和药物分子磷酰化后具有特殊的生物活性。我们已经利用Atherton-Todd反应合成了磷酰化氨基酸，并对酚羟基进行了磷酰化，发现它是一个有效的制取磷酸酯衍生物的方法。     

蛇肌果糖1,6-二磷酸酯酶的磷酰化部位与磷酰化条件

本文报道了从磷酰化的果糖1,6-二磷酸酯酶的胰蛋白酶水解物中分离得到了一个磷酰化的肽段及该肽段的氨基酸排列顺序和磷酰化的部位是在丝氨酸残基上。果糖1,6-二磷酸,果糖6磷酸和腺嘌呤核苷-磷酸等效应剂不影响该酶被无机正磷酸磷酰化。pH对磷酰化程度的影响和对酶活力的影响一致。磷酰化酶的活力比非磷酰化状态的酶活力稍低,活力的差别随着底物浓度的减小而增大。磷酰化的酶与Mg~(2+)和果糖1,6-二磷酸一起保温能脱磷酰化,本文结果进一步支持了蛇肌果糖1,6-二磷酸酯酶在催化果糖1,6-二磷酸水解的过程中,包含了形成磷酰化酶中间物这一过程。     

N—磷酰化二肽的分光光度法测定

利用双缩脲试剂，在可见光区建立了Ｎ－磷酰化二肽、二肽以及磷酰化多肽的分光光度定量分析方法。在经典的双缩脲分光光度法的实验条件下，观察到Ｎ－磷酰化二肽、二肽与双缩脲试剂的复合物的最大吸收波长均为６２０ｎｍ及Ｎ－磷酰基对二肽有很强的增色作用。     

苯并恶唑酮的磷酰化反应

苯并恶唑酮与六烷基亚磷酰胺, 乙氧基四烷基胺基亚磷酰胺和二(二烷基胺基)苯基膦的反应, 可得到O-确定磷酰化合物, 它们的结构通过IR, ^1H NMR , ^3^1P NMR,MS 和元素分析验证. 本文提出了形成这些化合物的可能的机理.     

苯并噻唑酮的磷酰化反应

本文研究了苯并噻唑酮与亚磷酸酯,六烷基亚磷酰胺及双-(二烷基胺基)苯基膦的反应,发现它不能与各种亚磷酸酯发生反应,与亚磷酰胺等反应生成N-磷酰化产物,在室温下观察到了P-N健的旋转阻滞现象,并对这种现象进行了讨论。     

Vitamin K脉冲辐解与激光光解的研究(Ⅱ)——VK3水溶液氧化反应时间分辨的研究

Vitamin K3(VK3)是很好的电子载体,文献[1,2]利用微秒级脉冲辐解研究了VK3水溶液体系,测定了一些自由基与VK3进行的单电子氧化还原反应及相关动力学参数.     

团聚铂纳米粒子电极在甲醇氧化中的电催化特性

用H2还原法并以Nafion作为稳定剂合成团聚的Pt纳米粒子，附载于玻碳表面制备电催化剂.透射电子显微镜（TEM）和扫描电子显微镜（SEM）表征结果指出,团聚Pt纳米粒子的平均尺寸约为400 nm.运用电化学循环伏安法(CV)和原位傅立叶变换红外反射光谱（in situ FTIRS）研究甲醇的氧化过程，发现团聚Pt纳米粒子电极具有较高的电催化活性.原位FTIRS研究结果检测到甲醇在所制备的电催化剂上氧化的中间体为线型吸附态CO物种，其红外吸收给出异常红外效应的光谱特征.     

Estimation of methionine and its metal complexes by oxidation with chloramine-T and dichloramine-T

A simple method for the estimation of methionine (HMt) in aqueous solution has been developed, based on its oxidation with chloramine-T and dichloramine-T at room temperature. The direct titration, with visual or potentiometric end-point involves a two-electron change, corresponding to the formation of methionine sulphoxide. Most amino-acids do not interfere, but cysteine, glutathione and thiourea are oxidized under these conditions. A back-titration procedure in which methionine is oxidized in 0.1M sodium hydroxide by excess of chloramine-T with a four-electron change corresponding to the formation of methionine sulphone has also been developed. Methionine is oxidized to the respective nitrile, however, with excess of dichloramine-T. The methods have also been employed in estimating methionine in two of its soluble complexes, [NiMt]ClO(4) and Na[AgMt(2)].     

Synthesis and Biological Activities of N-Phosphoryl Branched Peptides

Much research has shown that some N-phosphoryl peptides are endowed with important biological activities. For instance, Na-(diaryloxyphosphoryl)-L-alanyl-L-prolines are moderate inhibitors of angiotensin converting enzyme and yield highly potent inhibitors when they hydrolyze under physiological condition lossing 1 mol phenol1; Phosphoramido (N-[(a-rhamnopyranosyloxy)hydroxyphosphinyl]-L-Leu-L-Trp) and its analogues have been shown to be inhibitors of endothelin converting enzyme, therefor…     

N-磷酰化多巴胺与溶菌酶相互作用的ESI-MS研究

采用电喷雾离子肼-质谱(ESI-MS)研究了一系列结构具有可比性的N-磷酰化多巴胺与溶菌酶的非共价相互作用, 比较了磷上不同取代基对相互作用的影响. 结果表明, 磷上的烷氧取代基上烷基碳原子的个数及排列顺序对二者相互作用有较大影响; 取代基上碳链越长, 溶液中溶菌酶的构象越趋于收缩, 二者之间越容易形成带低电荷和高质核比的复合物, 且其稳定性也随着取代基的增长而增强; 当取代基碳原子数相同时, 直链取代的磷酰化多巴胺与溶菌酶形成的复合物比支链取代的底物与溶菌酶形成的复合物稳定.     

Determination of sulfur amino acids in foods as related to bioavailability

During the processing of feedstuffs and foods, methionine can be oxidized to methionine sulfoxide and methionine sulfone, and cysteine can be oxidized to cysteic acid. Methionine sulfone and cysteic acid are nutritionally unavailable, but methionine sulfoxide can be utilized, at least to some degree. The degree of utilization depends on the levels of methionine, cysteine, and methionine sulfoxide in the diet, but there is no consensus in the literature on the quantitative impact of these dietary constituents on methionine sulfoxide utilization. Methionine and cysteine are most often determined after quantitative oxidation to methionine sulfone and cysteic acid, respectively, using performic acid oxidation prior to hydrolysis. However, this method may overestimate the methionine content of processed foods, as it will include any methionine sulfoxide and methionine sulfone present. A selection of analytical methods has been developed to allow the separate determination of the 3 oxidized forms of methionine, the merits of which are discussed in this review. An additional consideration for determining methionine and cysteine bioavailability is that not all dietary methionine and cysteine is digested and absorbed from the small intestine. Selected methods designed to determine the extent of digestion and absorption are discussed. Finally, a concept for a new assay for determining methionine bioavailability, which includes determining the digestibility of methionine and methionine sulfoxide as well as the utilization of methionine sulfoxide, is presented.     

Electrochemical oxidation of sulfur-containing amino acids on an electrode modified with multi-walled carbon nanotubes

MWNT-modified electrodes are introduced for the voltammetric determination of sulfur-containing amino acids. The morphology of the electrode surface has been characterized by atomic force microscopy. The MWNT layer consists of deeply intertwined vermicular structures with the average diameter of 25 nm. Cysteine, glutathione and methionine are oxidized on the electrode while only cysteine gives signals on the glassy carbon (GC) electrode. The application of such electrodes leads to a decreased overpotential and increase of oxidation currents for cysteine in comparison with a bare GC electrode. The schemes of oxidation are proposed. A decrease of the lower limit of determination and an enlargement of the analytical range for antioxidants were obtained. A simple, fast and accurate procedure for the voltammetric determination of methionine in pharmaceuticals has been developed and can be recommended for quality control purposes.     

Oxidation of methionine residues in aqueous solutions: free methionine and methionine in granulocyte colony-stimulating factor

The free energy barriers and a mechanism of the oxidation of the amino acid methionine in water and in granulocyte colony-stimulating factor (G-CSF) are analyzed via combined quantum mechanical and molecular mechanical (QM/MM) methods, constrained molecular dynamics, and committor probability calculations. The computed free energy barrier of free methionine amino acid is very close to the measured value (14.7 +/- 1.2 versus 15.5 +/- 0.02 kcal/mol). The reaction coordinate was found to be the difference between the O-O bond of H2O2 and the S-O bond, where the S is the sulfur atom of the methionine residue. It was confirmed by computing the committor probability distribution and the distribution of constrained forces that this coordinate is not coupled to the activation of other degrees of freedom. The computed free energies of the oxidation of methionine residues in G-CSF indicate that the protein environment has insignificant effects on the reaction barriers of oxidation. This result further validates our proposal that the access of solvent to methionine sites, as measured by the two-shell water coordination number, governs the kinetics of the oxidation reaction of methionine groups in a protein molecule. We also found that the number of hydrogen bonds between the distal oxygen of H2O2 and the water molecules near the methionine increases along the reaction coordinate as oxidation progresses, indicating that the charge separation developed during the oxidation by H2O2 is stabilized by specific interactions with water molecules, such as hydrogen bonding.     

Phosphorylation of alcohols with N-phosphoryl oxazolidinones employing copper(II) triflate catalysis

[reaction: see text]. Phosphoryl transfer from N-phosphoryl 5,5-diphenyl oxazolidinone is efficiently catalyzed by copper(II) triflate. The utility of this method has been demonstrated in the phosphorylation of representative primary, secondary, tertiary, phenolic, and allylic alcohols. These reaction conditions are significantly milder than employing alkoxides and allow the phosphorylation of biologically relevant molecules.