修饰聚合物液-固亲和萃取体系纯化大豆中的组氨酸

聚乙二醇(PEG)6000经亚氨基二乙酸(IDA)修饰后和CuSO4反应,形成PEG修饰聚合物PEG-(IDA-Cu)2 ,与吐温80、磷酸盐混合,构成液-固亲和萃取体系,直接从大豆蛋白匀浆中提取氨基酸.选定萃取条件为磷酸盐摩尔比n(K2HPO4)∶n(NaH2PO4)为4.8∶1,体系pH值 7.70,总盐浓度为1.60 mol·L-1;吐温80的体积分数为10.5%.结果表明该体系对大豆蛋白匀浆中氨基酸的二次萃取率为66.5%,用离子交换技术后继处理,得纯度较高的组氨酸.     

铜锌超氧化物歧化酶的金属重组酶的活性部位与组氨酸的相互作用

应用核磁共振和电子自旋共振技术研究了铜锌超氧化物歧化酶（ＣｕＺｎＳＯＤ）的金属重组酶与水溶液中游离组氨酸（Ｈｉｓ）的相互作用。发现在水溶液中ＣｕＺｎＳＯＤ的金属重组酶活性中心的金属可与加入的Ｈｉｓ发生作用而被部分地诱导出来，与Ｈｉｓ形成络合物。     

Novel alginate-poly(L-histidine) microcapsules as drug carriers: in vitro protein release and short term stability

Spherical, smooth-surfaced and mechanically stable alginate-poly(L-histidine) (PLHis) microcapsules with narrow particle size distributions were prepared by incubating calcium alginate beads in aqueous solutions of PLHis. The in vitro release characteristics, drug loading and encapsulation efficiency of the microcapsules were investigated using bovine erythrocytes hemoglobin (Hb) as a model drug. The results showed that the concentration of Ca(2+) ions had a considerable effect on the drug loading, encapsulation efficiency and in vitro release behavior of the microcapsules. When the concentration of CaCl(2) in the PLHis solution was increased from 0 to 3.0% (w/v), the drug loading and encapsulation efficiency decreased significantly from 38.0 to 4.3% and from 92.9 to 8.0%, respectively, while the total cumulative release of Hb from microcapsules in phosphate buffered saline solution (PBS, pH 6.8) decreased from 96.2 to 72.8% in 24 h. No significant protein release was observed during 70 h of incubation in hydrochloric acid solution (pH 1.2). However, under neutral conditions (PBS, pH 6.8), the Hb was completely and stably released within 24-70 h. An explosion test showed that the stability of alginate-PLHis microcapsules depended strongly on the concentration of PLHis and the calcium ions in solution. [Diagram: see text] Microscopy photo of Hb-loaded alginate-PLHis microcapsules.     

L-histidine decarboxylase as a probe in studies on histamine

Because the Falck-Hillarp formaldehyde fluorescence method, which was superbly applied to identify catecholaminergic and serotonergic neurons, is not applicable to histamine, the first author (T.W.) developed an antibody to L-histidine decarboxylase (HDC) for identification of the histaminergic neuron system in the brain. The anti-HDC antibody was of great use for mapping the location and distribution of this histaminergic neuron system. (S)-alpha-fluoromethylhistidine, a specific and potent irreversible inhibitor of HDC, was also very useful in studies on functions of the neuron system. The activity of HDC is increased by various agents, treatments, and physiological conditions. We found new compounds that increased HDC activity (i.e., tetradecanoylphobol acetate (TPA), other tumor promoters, and staphylococcal enterotoxin A); and using mast cell-deficient mutant (W/W(v)) mice, we obtained evidence that this increase occurred in macrophages. To further characterize the mechanism of increases in HDC activity, the second author (H.O.) cloned human HDC cDNA and a human HDC gene. In studies on the regulation mechanism of the HDC gene, which is expressed only in limited types of cells such as mast cells, enterochromaffin-like cells in the stomach, cells in the tuberomammillary nucleus of the brain, and macrophages, CpG islands in the promoter region of the HDC gene were found to be demethylated in cells expressing the gene, whereas they are methylated in other cells that do not express the HDC gene. In collaboration with many other researchers, we developed HDC knockout mice. The resulting research is producing a lot of interesting findings in our laboratory as well as in others. In summary, HDC has been and will be useful in studies on functions of histamine.     

磷酰氨基酸的酯交换反应研究

本文利用^3^1P NMR , 对比研究了磷酰化组氨酸与其它磷酰化氨基酸和一级醇的磷上酯交换的反应速度,实验表明磷酰化组氨酸的反应速度最快. 由此提出了以下机理:由于咪唑环的参与,磷可以形成六配位过渡态,从而加快了反应速度.     

Role of Alginate Composition on Copper Ion Uptake in the Presence of Histidine or Beta-Amyloid

The anomalous interaction between metal ions and the peptide beta-amyloid is one of the hallmarks of Alzheimer’s disease. Metal-binding biopolymers, including polysaccharides, can elucidate the fundamental aspects of metal ions’ interactions with biological tissue and their interplay in Alzheimer’s disease. This work focuses on the role of the alginate composition on Cu(II) adsorption in the presence of histidine or β-amyloid, the peptide associated with the progression of Alzheimer’s disease. Alginate samples with different mannuronic/guluronic (M/G) ratios led to similar Cu(II) adsorption capacities, following the Langmuir isotherm and the pseudo-second-order adsorption kinetic models. Although the presence of histidine produced up to a 20% reduction in the copper adsorption capacity in guluronic-rich alginate samples (M/G~0.61), they presented stable bidentate chelation of the metallic ion. Chemical analyses (FTIR and XPS) demonstrated the role of hydroxyl and carboxyl groups in copper ion chelation, whereas both crystallinity and morphology analyses indicated the prevalence of histidine interaction with guluronic-rich alginate. Similar results were observed for Cu(II) adsorption in alginate beads in the presence of beta-amyloid and histidine, suggesting that the alginate/histidine system is a simple yet representative model to probe the application of biopolymers to metal ion uptake in the presence of biological competitors.     

Site‐specific reversible immobilization and purification of His‐tagged protein on poly(2‐acetamidoacrylic acid) hydrogel beads

Ni²⁺‐complexed poly(2‐acetamidoacrylic acid) (PAAA) hydrogel beads were developed for the site‐specific reversible immobilization and purification of the histidine‐tagged green fluorescent protein (His‐tagged GFP). PAAA hydrogel beads were prepared by photopolymerization, and significantly improved mechanical properties of PAAA hydrogel beads were observed in comparison with PAAA hydrogel from our previous study. Confocal laser scanning microscopy was used to determine the binding of His‐tagged GFP to the hydrogel beads in three‐dimensional space. Photoluminescence spectroscopy revealed 89% of binding efficiency of His‐tagged GFP to the Ni²⁺‐PAAA hydrogel beads, 51% of yielding recovery. The maximum binding capacity of His‐tagged GFP was estimated to be 0.45 µg/mg of Ni²⁺‐PAAA hydrogel beads. The recombinant His‐tagged GFP from the soluble fraction of E. coli BL21(DE3) cell lysates was purified with Ni²⁺‐PAAA hydrogel beads. The major advantage of the Ni²⁺‐PAAA hydrogel beads system was simple preparation procedures of producing the matrix, because PAAA hydrogel beads had relatively enhanced mechanical strength than soft hydrogels. Copyright © 2012 John Wiley & Sons, Ltd.     

pH‐Dependent Coordination of AgI Ions by Histidine: Experiment,Theory, and a Model for SilE

Artificial implants and biomaterials lack the natural defense system of our body and, thus, have to be protected from bacterial adhesion and biofilm formation. In addition to the increasing number of implanted objects, the resistance of bacteria is also an important problem. Silver ions are well‐known for their antimicrobial properties, yet not a lot is known about their mode of action. Silver is expected to interact on many levels, thus the development of silver resistance is very difficult. Nevertheless, some bacteria are able to resist silver, even at higher concentrations. One such defense mechanism of bacteria against heavy‐metal intoxication includes an efflux system. SilE, a periplasmic silver‐binding protein that is involved in this defense mechanism, has been shown to possess numerous histidine functions, which strongly bind to silver atoms, as demonstrated by ourselves previously. Herein, we address the question of how histidine binds to silver ions as a function of pH value. This property is important because the local proton concentration in cells varies. Thus, we solved the crystal structures of histidine–silver complexes at different pH values and also investigated the influence of the amino‐acid configuration. These results were completed by DFT calculations on the binding strength and packing effects and led to the development of a model for the mode of action of SilE.     

Can Co(II) or Cd(II) substitute for Zn(II) in zinc fingers?

Zinc finger domains consist of sequences of amino acids containing cysteine and histidine residues tetrahedrally coordinated to a zinc ion. The role of zinc in a DNA binding finger was considered purely structural due to the absence of redox chemistry in zinc. However, whether other metals e.g. Co(II) or Cd(II) can substitute Zn(II) is not settled. For an answer the detailed interaction of Co(II) and Cd(II) with cysteine methylester and histidine methylester has been investigated as a model for the zinc core in zinc fingers. The study was extended to different temperatures to evaluate the thermodynamic parameters associated with these interactions. The results suggest that zinc has a unique role.     

Model studies of trialkyltin–protein interactions: 13C NMR analysis of solution equilibria of the complex between trimethyltin and methyl N-benzoyl-l-leucyl-l-histidinate

¹³C NMR spectra for the 1:1 complex between methyl N-benzoyl-l-leucyl-l-histidinate and the trimethyltin moiety in d-chloroform (CDC1₃), d₄-methanol (CD₃OD) dimethyl sulphoxide (DMSO) and d₆-DMSO/H₂O solvents are reported, and contrasted with those for the free ligand. The spectra are interpreted in terms of a variety of solution equilibria illustrating the nature of the interaction between the trimethyltin species and primarily the imidazole ring of the histidine residue. Evidence for the preferential stability of pentacoordinate solution structures about tin is presented.