聚合酶链反应检测乳酸菌酪氨酸脱羧酶基因

酪氨酸脱羧酶与乳酸菌发酵食品中酪胺的产生密切相关。根据从GenBank中检索到的酪氨酸脱羧酶基因序列设计一对特异性引物，采用PCR技术对乳酸菌的基因组DNA片段进行扩增，以此建立以酪氨酸脱羧酶基因为靶的产酪胺乳酸菌的分子生物学检测方法。结果表明，供试12株乳酸菌中有9株菌扩增出1133bp DNA片段对其中3株菌的扩增产物进行DNA序列测定，测序结果采用国际互联网上NCBI的BLAST工具进行同源性检索分析，发现它与已知的Enteroeoeeus faecalis，Enterococcus faecium，Canmbacterium divergens的酪氨酸脱羧酶基因序列均高度同源，其中PLP(5’-磷酸吡哆醛)的结合位点高度保守，证明该扩增产物是酪氨酸脱羧酶的基因片段。应用该法与常规平板检测法比较显示，二者检测结果基本一致，表明本研究建立的PCR方法可作为一种快速、高度特异的检测产酪胺乳酸菌菌株的新方法。     

Evidence of horizontal transfer as origin of strain to strain variation of the tyramine production trait in Lactobacillus brevis

Lactobacillus brevis strains with the ability to decarboxylate tyrosine to tyramine have been described and the involvement of several genes constituting a tyrdc operon at the chromosomal level has been demonstrated in this species. In this study, the existence of Lb. brevis strains unable to form tyramine was observed. In order to evaluate if the tyramine-producing ability was strain-dependent or if it could be correlated to the existence of a new species or subspecies, different isolates were analysed. Analysis by M13-RAPD and sequencing of 16S rDNA, 16S–23S ISR and house-keeping gene recA confirmed that all the isolates belonged to the Lb. brevis species. Analysis of the TyrDC pathway encoding operon region in representative strains indicated the existence of a polymorphism. The genetic differences observed showed that the tyrosine decarboxylating ability is not a Lb. brevis species trait but that it is strain-dependent within this species and suggest that the genes encoding the tyramine-producing pathway constitute a genomic island.     

色氨酸、酪氨酸对胸腺嘧啶辐射损伤的影响及其作用机理的研究

用紫外分光光度法、CNDO/2理论计算研究了色氨酸和酪氨酸对胸腺嘧啶的辐射保护与敏化作用,其作用机理是:在常温水溶液体系中是清除水辐解自由基;而在冰冻水溶液体系中,电荷转移和激发能转移则是主要的。     

胰岛素受体酪氨酸蛋白激酶对醛糖还原酶的磷酸化作用

从人胎盘纯化了醛糖还原酶和部分纯化了胰岛素受体。通过磷酸化实验证明：醛糖还原酶是胰岛素受体酪氨酸蛋白激酶的底物，经分析揭示：胰岛素受体酪氨酸蛋白激酶可将醛糖还原酶的第４０位和第４９位的酪氨酸残基磷酸化。在试管内，未磷酸化的醛糖还原酶和磷酸化的醛糖还原酶的动力学常数无差异，而细胞内的情况有待于进一步研究，本实验提示：醛糖还原酶除具酶活性外，可能还有在细胞内传递胰腺素信息的功能。     

三酶偶联全细胞生物合成L-酪氨酸

通过将醛缩酶(ALD)、D-丝氨酸脱水酶(SDH)和酪氨酸酚裂解酶(TPL)三酶偶联,催化甘氨酸、甲醛和苯酚合成L-酪氨酸(L-Tyr)。并以L-Tyr的质量浓度为指标对转化工艺进行了考察。结果表明:三酶偶联最佳反应条件为pH=8.5、温度35℃、乙酸铵质量分数6 g/L、磷酸吡哆醛(PLP)质量浓度0.1 g/L、3种酶细胞配比m(ALD)∶m(SDH)∶m(TPL)=6∶3∶5。当甘氨酸加量为50 g/L,利用上述工艺进行10000 L放大,反应11 h,L-Tyr质量浓度可达117 g/L,苯酚转化率为97%,转化体系放大后苯酚转化率提高4%,收率为85%。     

Silver-Nanoparticle-Embedded Short Amphiphilic Peptide Nanostructures and Their Plausible Application to Reduce Bacterial Infections

The microbiota-gut-brain axis (GBA) plays a critical role in the development of neurodegenerative diseases. Dysbiosis of the intestinal microbiome causes a significant alteration in the gut microbiota of Alzheimer's disease (AD) patients, followed by neuroinflammatory processes. Thus, AD beginning in the gut is closely related to an imbalance in gut microbiota, and hence a multidomain approach to reduce this imbalance by exerting positive effects on the gut microbiota is needed. In one example, a tyrosine-based short peptide amphiphile (sPA) was used to synthesize antibacterial AgNPs−sPA nanostructures. Such nanostructures showed high biocompatibility and low cytotoxicity, and therefore work as model drug delivery agents for addressing local bacterial infections. These may have therapeutic value for the treatment of microbiota-triggered progression of neurodegenerative diseases.     

Experimental and Theoretical Investigation of Double Gas Hydrate Formation in the Presence or Absence of Kinetic Inhibitors in a Flow Mini‐Loop Apparatus

Double gas hydrate formation in the presence or absence of kinetic inhibitors in a flow mini‐loop apparatus was investigated. For the prediction of the gas consumption rate during hydrate formation in this system, the rate equation based on the Kashchiev and Firoozabadi model for simple gas hydrate formation in a batch system was developed for double gas hydrate formation in a flow mini‐loop apparatus. To complete the theoretical evaluation of gas hydrate formation through the mini‐loop apparatus in the presence or absence of kinetic hydrate inhibitors (KHI), a laboratory flow mini‐loop apparatus was set up to measure the induction time for hydrate formation and the uptake rate when a gaseous mixture (such as 75 % C1/25 % C3, 25 % C1/75 % C3, 75 % C1/25 % i‐C4, and 25 % C1/75 % i‐C4) is contacted with water containing or not containing dissolved inhibitor under suitable temperature and pressure conditions. In each experiment, a water blend saturated with gas mixture was circulated up to the required pressure. The pressure was maintained at a constant value during the experimental runs by means of a required gas mixture make‐up. The effect of pressure on gas consumption during hydrate formation was investigated in the presence or absence of polyvinylpyrrolidone (PVP) and L ‐tyrosine as kinetic inhibitors at various concentrations. A good agreement was found between the predicted and experimental data in the presence or absence of KHI. The total average absolute deviation percents between the experimental and predicted values of gas consumption were found to be 16.4 and 17.5 % for the double gas hydrate formation in the presence or absence of the kinetic inhibitors, respectively.     

Tyrosine metabolism in pigment-forming Yarrowia lipolytica strains isolated from English and European speciality mould-ripened cheese exhibiting a brown discolouration defect

Yarrowia lipolytica s4fd was isolated from a UK-manufactured speciality mould-ripened cheese as the causative micro-organism of a brown surface discolouration spoilage defect. Comparative studies utilizing Y. lipolytica isolates indicated that inter-strain variations in pigment accumulation were attributable to differences in tyrosine uptake and metabolism to homogentisic acid. The range and activity profiles of proteolytic enzymes involved in tyrosine release and turnover in isolates that differed in pigment formation were, however, similar. Homogentisic acid formation was affected by physiological parameters, and approaches that may be developed by the cheesemaker to prevent spoilage losses associated with the development of the brown discolouration defect are discussed.     

Application of L-DOPA modified carbon nanotubes as a bifunctional electrocatalyst for simultaneous determination of ascorbic acid,adrenaline, acetaminophen and tyrosine

L-DOPA multi-wall carbon nanotube modified glassy carbon electrode (DOPA-MWCNT-GCE) was used as a bifunctional electrocatalyst for simultaneous quantitative determination of ascorbic acid (AA) and adrenaline (AD). Electrochemical experiments show that the modified electrode plays the role of an excellent bifunctional electrocatalyst for the oxidation of AA and AD in two different potentials. The kinetic parameters such as the electron transfer coefficient, α, and the heterogeneous electron transfer rate constant, k′, for the electrocatalytic oxidation of AA and AD at the DOPA-MWCNT-GCE surface were estimated. Through a different pulse voltammetric (DPV) method, the plot of the electrocatalytic current versus AA and AD concentrations emerged to be constituted of two linear segments with different sensitivities. In addition, detection limits of 1.5 μM for AA and 0.62 μM for AD were obtained. In DPV, the proposed bifunctional electrocatalyst could separate the oxidation peak potentials of AA, AD, acetaminophen (AC) and tyrosine (Tyr) present in a mixture though, at the bare GCE, the peak potentials overlap. Finally, DOPA-MWCNT-GCE was satisfactorily used for the determination of AA, AD, AC and Tyr in pharmaceutical preparations.     

基于钴(Ⅱ)-酪氨酸络合作用的酪氨酸极谱法分析研究

在0.02mol/L硼酸盐缓冲溶液(pH8.7)中,钴(Ⅱ)与酪氨酸生成的络合物在-0.82V(vs.SCE)有一阴极极谱还原峰。基于该极谱行为建立了酪氨酸的分析体系并进行实验条件优化,其浓度在8.0×10-5至4.0×10-4mol/L之间与极谱峰电流呈良好线性关系,检出限为2.8×10-6mol/L。