Quantitative Determination Of Tyrosine Research Articles

An Endoscope-like SERS Probe Based on the Focusing Effect of Silica Nanospheres for Tyrosine and Urea Detection in Sweat.

In this work, we developed a new type of SERS probe, which was composed of glass-SiO2-Au@MBN@Ag nanoparticles (NPs) three-dimensional Surface-enhanced Raman spectroscopy (SERS) substrate. When the laser passed through the quartz glass sheet, on the one hand, the SiO2 NPs supporting the Au@MBN@Ag NPs increase the roughness of the substrate surface, resulting in a large number of hot spots among nanoparticles. On the other hand, based on the focusing effect of silicon dioxide nanospheres, the laser can better focus on the surface of nanoparticles in the inverted SERS probe, thus showing better SERS enhancement. Furthermore, the Au@MBN@Ag NPs core-shell structure was used with 4-mercaptobenzoonitrile (MBN) as an internal standard molecule, and the quantitative determination of tyrosine and urea was realized by internal standard correction method. The standard working curves of the two had good linear correlation with R2 above 0.9555. The detection limits of tyrosine and urea were in the range of 2.85 × 10−10 M~7.54 × 10−6 M, which confirms that this design can be used for quantitative and specific detection of biological molecules, demonstrating great practical significance for the research of diseases such as skin lesions and endocrine disorders.

Screening of Enzyme Producers with Keratinase Activity among Marine Actinobacteria

About 2 million tons of feathers are produced annually around the world as a by-product of poultry farming. Due to the lack of funds and the complexity of processing, they have become one of the main environmental pollutants. The biodegradation of feathers by keratinolytic microorganisms has proven to be an effective, environmentally friendly and cost-effective method of bioconverting feather waste into a nutritious, balanced and easily digestible product that contains free amino acids, peptides and ammonium ions. Aim. To investigate the ability of marine actinobacteria to synthesize enzymes with keratinolytic activity and to study some of the physicochemical properties of the most active enzyme preparation. The object of the study was 10 strains of actinobacteria isolated from bottom sediments in the area of the Pradneprovsky trench of the Black Sea shelf. Methods. Caseinolytic (general proteolytic) activity was determined by the Anson method modified by Petrova, based on the quantitative determination of tyrosine, which is formed during the enzymatic hydrolysis of casein. Keratinase activity was determined by UV absorption at 280 nm of the hydrolysis products of keratin-containing raw materials. The cultivation of actinobacteria was carried out in a liquid nutrient medium with the addition of defatted chicken feathers as the main source of carbon and nitrogen. Results. The ability to hydrolyze keratin was found in five cultures. Moreover, all the strains studied were practically unable to break down casein. The Acty 9 strain (12 U/ml) showed the highest keratinase activity. Additional introduction of NaCl to the nutrient medium did not have a positive effect on the enzymes synthesis. The study of the physicochemical properties of the enzyme preparation Acty 9 showed that the pH and thermooptimum were 9.0 and 60°C, respectively. It retained 100% of the initial activity in the range of pH 7.0–10.0 after 3 h and 95% activity at pH 8.0 after 24 h of incubation. The studied enzyme preparation was thermostable, since it remained active for 3 h at 50°C and 1 h at 60°C. Conclusions. The extracellular keratinase synthesized by actinobacterium Acty 9 is promising for further research, since the enzyme is pH and thermostable and is not inferior in its physicochemical properties to those previously described in the literature.

Chiral recognition and quantitative analysis of tyrosine enantiomers using L-cysteine capped CdTe quantum dots: Circular dichroism, fluorescence, and theoretical calculation studies

In this work, L-cysteine-capped CdTe quantum dots (L-Cys/CdTe QDs) were used as novel chiral probes for in enantioselective recognition and quantitative determination of tyrosine (Tyr) enantiomers using both fluorescence and circular dichroism (CD) spectroscopies. Different quenching percentages in fluorescence of L-Cys/CdTe QDs in the presence of similar concentrations of Tyr enantiomers were clearly observed. Quantum mechanical (QM) calculations were also used to confirm such different interactions of L- and D-Tyr enantiomers with L-Cys/CdTe QDs. However, the CD spectroscopy exhibited higher capability and sensitivity, compared to fluorescence spectroscopy, to distinguish between these enantiomers. While, Tyr enantiomers provided no sensible CD signals at micromolar concentration levels, they exhibited remarkable and opposite CD spectra at these concentration levels in the presence of L-Cys/CdTe QDs. Under the optimized conditions, the CD signals of L- and D-Tyr enantiomers showed good linear relationships with the concentrations of both enantiomers over the range of 10–80 µM with limit of detections (LODs) of 1.5 and 1.6 µM, respectively. This method was also successfully applied to enantiomeric excess determination of Tyr at the total concentration of 50 μM with a LOD of 1.2%.

Fluorescence assay of tyrosine in blood plasma

A more simple and sensitive assay for the quantitative determination of tyrosine in blood plasma is developed on the basis of a modification of the method of S. Udenfriend (1962). A volume of 0.2 ml of plasma is used in the analysis; after its deproteinization with trichloroacetic acid, it is reacted with sodium nitride, nitrous acid, and 1-nitroso-2-naphthol at 65°C, and the content of the reaction product is measured by the fluorescence at λex/λem=460/570 nm. The consumption of plasma and reagents is reduced by a factor of 5–10 compared to the original method; in addition, the stage of extraction with an organic solvent is excluded. The linear dependence of the fluorescence signal on the tyrosine concentration within the range of 2–60 μg/ml, high specificity, accuracy, and reproducibility of the assay are shown. The importance of tyrosine determination in monitoring of glucocorticoid therapy and protein catabolism is discussed.

A rapid quantitative analysis of tyrosine and its oxidation products by tyrosinase.

A new technique based on liquid phase ion exchange chromatography on short column is proposed for quantitative determination of tyrosine and Dopa. alpha-Amino,beta-guanidinopropionic acid is used as an internal standard of coloration. The role of H2O2 and ascorbic acid on tyrosine and Dopa was checked. Ascorbic acid prevents the auto-oxidation of Dopa, H2O2 has no effect on tyrosine but oxidizes Dopa even in the presence of excess ascorbic acid. This method was tested in mushroom tyrosinase, with and without ascorbic acid. Assays performed with tyrosinase from rabbit ocular extracts clearly showed that they do oxidize tyrosine. Reliability of the method is comparable to radioassay.

Magnetic circular dichroism studies: XIX. Determination of the tyrosine: Trytophan ratio in proteins

Recently (2), we reported the use of magnetic circular dichroism (MCD) for the determination of tryptophan in intact proteins (1). We pointed out that, in comparison to other methods currently in use, MCD has the unique advantage of giving unambiguous results even in cases in which the tyrosine: tryptophan ratio is high, that conformational and environmental effects do not interfere with the accuracy of the method, and that only small amounts of sample are required. Here, we wish to report an important refinement in the procedure that enables the technique to be extended to samples which, due to the presence of unknown quantities of water or inorganic salts, are not of analytical purity. This modification makes use of the fact that, in contradistinction to tryptophan, the quantitative determination of tyrosine by the usual chromatographic procedure subsequent to hydrolytic cleavage of the protein does not present serious difficulties. Consequently, the spectroscopic determination of the tyrosine: tryptophan ratio has the advantage that, given knowledge of the tyrosine content, accurate values for the tryptophan content can be obtained with only rough knowledge of the protein concentration. Thus, tyrosine serves as an internal standard in the determination of tryptophan by the MCD technique. In addition to enabling tryptophan determinations to be made with increased accuracy, this modification illustrates the advantages inherent in a spectroscopic method in which signals may occur with either positive or negative sign.

The quantitative determination of tyrosine, 3-iodotyrosine and 3,5-diiodotyrosine in iodinated insulin preparations

The quantitative determination of tyrosine, 3-iodotyrosine and 3,5-diiodotyrosine in iodinated insulin preparations