分光光度法测定水母雪莲细胞培养物中的总黄酮

建立了测定水母雪莲细胞培养物中的总黄酮含量的分光光度法,该法操作简便,结果准确可靠。     

紫外分光光度法测定甘草黄酮含量

采用分光光度法,测定了甘草中总黄酮的合量,检测波长为500nm,标准曲线相关系数R^2为0．9994,相对标准偏差为0．20％,平均加样回收率为100．20％。结果表明,此法准确度较高,为甘草生药及成品药中甘草黄酮合量测定提供了一种切实可行的方法     

紫外可见分光光度法测定杜仲绿原酸含量的方法研究

目前,测定绿原酸含量的方法很多,常采用毛细管电泳法、ＨＰＬＣ法、可见分光光度法和纸层析-紫外可见分光光度法等[1,2,3,4]。但样品处理均采用索氏回流提取,后经层析分离洗脱等步骤,时间长、效率低。本文采用紫外可见分光光度法测定绿原酸含量,只需超声波提取一小时,不经...     

变色酸-分光光度法测定丝氨酸含量

建立了变色酸-分光光度法测定丝氨酸含量的方法。丝氨酸在一定的pH条件下经高碘酸钠氧化后能与变色酸发生发应,产物在570 nm处有最大吸光值,且吸光值与丝氨酸的含量呈一次线性关系。结果表明,丝氨酸在0-1.0 g.L-1范围内呈良好的线性关系(r=0.9973),平均加样回收率为100.30%,RSD为1.11%。将测量结果与高效液相测量结果做比较,两种方法的相符率达到99%至101%。变色酸-分光光度法操作简便,结果准确。     

分光光度法测定叶绿素含量及其比值问题的探讨

本文以水稻、棉花、玉米以及喜荫植物吉祥草为材料,采用分光光度法比较了不同性能的分光光度计对叶绿素含量及其比值测定的影响。结果表明,狭缝宽度过小或过大均导致叶绿素定量结果的相对误差增大,但仪器的波长偏移是引起测定结果误差的主要原因。波长偏差超过1nm时会影响混合溶液中叶绿素b的定量结果以及叶绿素的相对比值（Chla／Chlb）,波长“蓝移”引起Chla／Chlb偏高,波长“红移”则导致Chla／Chlb偏低。波长偏移及波长重现性差是造成Chla／Chlb比值偏离其“理论比值”、导致测定数据之间缺少可比性的原因。选择具有波长自动校准功能、波长精度高、狭缝宽度在1-2nm的分光光度计用于叶绿素含量及其比值的测定则可获得可比性强、重现性好、准确度高的结果。     

紫外分光光度法测定肉碱转化液中巴豆甜菜碱的含量

通过对巴豆甜菜碱和L－肉碱在紫外188－215mm的光吸收的比较,建立了紫外分光光度法测定肉碱转化液中巴豆甜菜碱含量的方法,测定波长205mm,线性范围0－25ug/ml,该方法快速方便 ,重复性好,可用于L－肉碱生产过程中巴豆甜菜碱的跟踪检测。     

桐柏野大豆种子粗蛋白质测定及方法探讨

野大豆因其高蛋白、低油脂含量等特点,越来越引起人们的关注。为了快速精确测定野大豆粗蛋白质含量,采用半微量凯氏法和消化—分光光度法对采自桐柏的8个野大豆样品进行蛋白质含量的测定,并分析比较两种测定方法。试验结果显示,采用消化—分光光度法测定的野大豆的蛋白质含量与经典的半微量凯氏法测定结果一致。半微量凯氏法适用范围广,测定结果精确,而消化—分光光度法相对于半微量凯氏法简化了试验操作,缩短了分析时间,又没有特殊的仪器设备和试剂要求,更便于普及应用。     

可见分光光度法测定杜仲叶中的绿原酸

研究杜仲叶中绿原酸含量的检测方法。利用绿原酸和铝离子的络合显色反应,采用可见分光光度法在波长530 nm处测定杜仲叶中绿原酸量。绿原酸质量浓度在1.7×10-4~1.0×10-2g.L-1之间线性关系良好,线性相关系数为0.9995。秋、夏叶中加标回收率分别为98.0%,101.0%。该方法简便、实用、准确。     

紫外分光光度法测定发酵液中L-天冬氨酸

建立测定发酵液中L-天冬氨酸的一种紫外分光光度测定方法,研究金属离子、反应时间、反应温度等对测定的影响,确定测定的最适条件,L-天冬氨酸溶液与茚三酮显色剂反应显蓝紫色,用紫外分光光度计对L-天冬氨酸反应溶液进行测定,得到最大吸收峰,根据最大吸收峰所对应的波长确定L-天冬氨酸吸光度与浓度间关系曲线。研究表明,L-天冬氨酸最佳吸收波长为510 nm,吸光度与浓度间工作曲线为:Y=0.067 8 X+0.013 5,r~2=0.999 5,反应时间和反应温度对检测无影响,其他金属离子均不干扰L-天冬氨酸的测定,紫外分光光度法测定发酵液中L-天冬氨酸的操作简便、快捷、准确。     

The role of tryptophan in the ferredoxin-dependent nitrite reductase of spinach

A system has been developed for expressing a His-tagged form of the ferredoxin-dependent nitrite reductase of spinach in Escherichia coli. The catalytic and spectral properties of the His-tagged, recombinant enzyme are similar, but not identical, to those previously observed for nitrite reductase isolated directly from spinach leaf. A detailed comparison of the spectral, catalytic and fluorescence properties of nitrite reductase variants, in which each of the enzyme’s eight tryptophan residues has been replaced using site-directed mutagenesis by either aromatic or non-aromatic amino acids, has been used to examine possible roles for tryptophan residues in the reduction of nitrite to ammonia catalyzed by the enzyme.     

Isolation,structure determination and cytotoxicity studies of tryptophan alkaloids from an Australian marine sponge Hyrtios sp.

Mass-guided fractionation of the MeOH extract from a specimen of the Australian marine sponge Hyrtios sp. resulted in the isolation of two new tryptophan alkaloids, 6-oxofascaplysin (2), and secofascaplysic acid (3), in addition to the known metabolites fascaplysin (1) and reticulatate (4). The structures of all molecules were determined following NMR and MS data analysis. Structural ambiguities in 2 were addressed through comparison of experimental and DFT-generated theoretical NMR spectral values. Compounds 1–4 were evaluated for their cytotoxicity against a prostate cancer cell line (LNCaP) and were shown to display IC₅₀ values ranging from 0.54 to 44.9 μM.     

The significance of tryptophan in human nutrition

Summary Aside from its role as one of the limiting essential amino acids in protein metabolism, tryptophan (TRP) serves as precursor for the synthesis of the neurotransmitters serotonin and tryptamine as well as for the synthesis of the antipellagra vitamin nicotinic acid and the epiphyseal hormone melatonin.By involvement in so manifold pathways, TRP and its metabolites regulate neurobehavioral effects such as appetite, sleeping-waking-rhythm and pain perception. TRP is the only amino acid which binds to serum albumin to a high degree. Its transport through cell membranes is competetrvely inhibited by large neutral amino acids (NAA). The TRP/NAA ratio in plasma is essential for the TRP availability and thus for the serotonin synthesis in the brain.Due to its high TRP-concentration, human milk protein provides optimal conditions for the availability of the neurotransmitter serotonin. Low protein cow's milk-based infant formulas supplemented with-lactalbumin — a whey protein fraction containing 5.8% TRP — present themselves as a new generation of formulas, with an amino acid pattern different from the currently used protein mixtures of adapted formulas, resembling that of human milk to a much higher degree.     

Action of tryptophan analogues in Saccharomyces cerevisiae

In an analysis of the effects of various tryptophan and indole analogues in Saccharomyces cerevisiae we determined the mechanisms by which they cause growth inhibition: 4-Methyltryptophan causes a reduction in protein synthesis and a derepression of the tryptophan enzymes despite of the presence of high internal levels of tryptophan. This inhibition can only be observed in a mutant with increased permeability to the analogue. These results are consistent with but do not prove an interference of this analogue with the charging of tryptophan onto tRNA. 5-Methyltryptophan causes false feedback inhibition of anthranilate synthase, the first enzyme of the tryptophan pathway. This inhibits the further synthesis of tryptophan and results in results in tryptophan limitation, growth inhibition and derepression of the enzymes. Derepression eventually allows wild type cells to partially overcome the inhibitory effect of the analogue. 5-Fluoroindole is converted endogenously to 5-fluorotryptophan by tryptophan synthase. Both endogenous and externally supplied 5-fluorotryptophan are incorporated into protein. This leads to intoxication of the cells due to the accumulation of faulty proteins. 5-Fluorotryptophan also causes feedback inhibition of anthranilate synthase and reduces the synthesis of tryptophan which would otherwise compete with the analogues in the charging reaction. Indole acrylic acid inhibits the conversion of indole to tryptophan by tryptophan synthase. This results in a depletion of the tryptophan pool which, in turn, causes growth inhibition and derepression of the tryptophan enzymes.Abbreviations cpm counts per minute - OD optical density at 546 nm - TCA trichloro acetic acid - tRNA transfer ribonucleic acid; trp1 to trp5 refer to the structural genes for the corresponding tryptophan biosynthetic enzymes - trpl^– res. trp1^± refer to mutant strains synthesizing completely resp. partially defective enzymes     

The quenching of tryptophan fluorescence by protonated and unprotonated imidazole

The fluorescence life-time of N-acetyl-tryptophan-amide (NATA) was measured by multifrequency phase fluorometry, in the presence of increasing concentrations of imidazole. Two pH values were tested, pH 4.5 where imidazole is fully protonated and pH 9.0 where it is fully unprotonated. At both pH values, the inverse life-time increases in a non-linear way with the imidazole concentration, showing that imidazole is not a high efficiency collisional quencher. The data can be analysed in terms of the formation of a complex with a reduced fluorescence life-time. The rate constants for association (at 25°C) are around 5 (±0.2) × 10⁹ M^–1 s^–1 and are thus diffusion controlled. The association equilibrium constant is strongly pH dependent and is much higher than the expected value of 0.4 M^–1 for a collisional complex. The intrinsic fluorescence life-time of the complex is 1.56 (±0.02) ns at pH 9.0 and 1.82 (±0.03) ns at pH 4.5, as compared to 2.37 (±0.03) ns for free NATA at pH 9.0 and 2.83 (±0.05) at pH 4.5 (all atI = 0.34). This means that at both pH values the fluorescence life-time of NATA in the complex is reduced to 61 (±0.5)% of its value in the free state. Despite this, the protonated form of imidazole is a better quencher at low concentrations, owing to a longer residence-time of the complex. At high viscosity the association equilibration is too slow and the system is described by two life-times. The quenching effect ofHis-18 on the fluorescence of the proximalTrp-94 of barnase (Locwenthal et al. 1991, Willaert et al. 1991) is discussed in terms of these findings.     

Capillary zone electrophoresis separation of tryptophan and its metabolites, including quinolinic acid

Capillary zone electrophoresis with UV absorbance detection was used to separate tryptophan and ten its metabolites. Run buffers of pH 4.0–10.0 were evaluated for their effect on resolution; a pH 9.6 buffer was found to give optimum separation of all components. Ethylenediaminetetraacetic acid (EDTA), which prevents complexation of some analytes with polyvalent cations, was included in the run buffer to insure good peak shape and reproducible mobilities. The resulting method was used to detect the presence of quinolinic acid in a urine sample.     

A simple colorimetric method for the determination of tryptophan

A simple, sensitive, and reproducible colorimetric method for the determination of tryptophan in amounts as low as 2 μg is described. It is based on the oxidation of tryptophan by sodium nitrite and the coupling of the oxidized product to the leucodye N-1-(naphthyl)ethylenediamine dihydrochloride. The purple-pink product has an absorption maximum at 550 nm. There is no interference by carbohydrates, other amino acids, neutral salts, or a number of other compounds likely to be found in tissue hydrolysates. A number of indole derivatives including indole-3-acetic acid also react to give a colored product. Dipeptides containing tryptophan are much less reactive than free tryptophan; hence proteins must be hydrolyzed completely for the method to be useful. The assay is carried out at room temperature and can be modified easily to increase or decrease its sensitivity. It has been employed to determine the tryptophan content of a number of proteins following alkaline hydrolysis. Generally, values obtained were in close agreement with values reported in the literature.