Presence Of Tyrosine Research Articles

Evolution of ion channels in cetaceans: a natural experiment in the tree of life

Cetaceans represent a natural experiment within the tree of life in which a lineage changed from terrestrial to aquatic habitats. This shift involved phenotypic modifications, representing an opportunity to explore the genetic bases of phenotypic diversity. Among the different molecular systems that maintain cellular homeostasis, ion channels are crucial for the proper physiological functioning of all living species. This study aims to explore the evolution of ion channels during the evolutionary history of cetaceans. To do so, we created a bioinformatic pipeline to annotate the repertoire of ion channels in the genome of the species included in our sampling. Our main results show that cetaceans have, on average, fewer protein-coding genes and a higher percentage of annotated ion channels than non-cetacean mammals. Signals of positive selection were detected in ion channels related to the heart, locomotion, visual and neurological phenotypes. Interestingly, we predict that the NaV1.5 ion channel of most toothed whales (odontocetes) is sensitive to tetrodotoxin, similar to NaV1.7, given the presence of tyrosine instead of cysteine, in a specific position of the ion channel. Finally, the gene turnover rate of the cetacean crown group is more than three times faster than that of non-cetacean mammals.

The importance of tyrosines in multimers of cyclic RGD nonapeptides: towards αvβ6-integrin targeted radiotherapeutics.

In a recent paper in this journal (RSC Med. Chem., 2023, 14, 2429), we described an unusually strong impact of regiospecific exchange of phenylalanines by tyrosines in 10 gallium-68-labeled trimers of certain cyclic RGD peptides, c[XRGDLAXp(NMe)K] (X = F or Y), on non-specific organ uptakes. We found that there was, in part, no correlation of liver uptake with established polarity proxies, such as the octanol-water distribution coefficient (log D). Since this observation could not be explained straightforwardly, we suggested that the symmetry of the compounds had resulted in a synergistic interaction of certain components of the macromolecules. In the present work, we investigated whether a comparable effect also occurred for a series of 5 tetramers labeled with lutetium-177. We found that in contrast to the trimers, liver uptake of the tetramers was well correlated to their polarity, indicating that the unusual observations along the trimer series indeed was a unique feature, probably related to their particular symmetry. Since the Lu-177 labeled tetramers are also potential agents for treatment of a variety of αvβ6-integrin expressing cancers, these were evaluated in mice bearing human lung adenocarcinoma xenografts. Due to their tumor-specific uptake and retention in biodistribution and SPECT imaging experiments, these compounds are considered a step forward on the way to αvβ6-integrin-targeted anticancer agents. Furthermore, we noticed that the presence of tyrosines in general had a positive impact on the in vivo performance of our peptide multimers. In view of the fact that a corresponding rule was already proposed in the context of protein engineering, we argue in favor of considering peptide multimers as a special class of small or medium-sized proteins. In summary, we contend that the performance of peptide multimers is less determined by the in vitro characteristics (particularly, affinity and selectivity) of monomers, but rather by the peptides' suitability for the overall macromolecular design concept, and peptides containing tyrosines are preferred.

Green Synthesis of Silver Nanoparticle from Brassica Oleracea for Determination of Paracetamol in the Presence of Tyrosine, Leucine and Alanine by Derivative Method

In this work, biogenic silver nanoparticles (Ag NPs) from Brassica oleracea (Bo) leaf extract (AgNP-Bo) were prepared and utilized in synthetic mixtures for the accurate, effective, and sensitive spectrophotometric detection of Paracetamol. Measurements in the UV-Visible, X-ray diffraction (XRD), and scanning electron microscopy (SEM) have been used to confirm the synthesis of AgNP-Bo. These statistics indicate that the average particle size is 26.39 nm, the crystallinity has an aggregated structure, and the typical absorption wavelength is 445 nm. To decrease the possible influence of the listed water-soluble interference analytes, namely Tyrosine, Alanine, and Leucine, the 2nd order derivative method was used for our investigation. Using complexation with AgNP-Bo, the linear range, limit of detection (LOD), and relative standard deviation (RSD) for Paracetamol were calculated. The obtained values were 0.1-2, 0.09 µM, and 1.06%, respectively. With average percent recovery values of 93.33, 96.67, and 90.00%, respectively, AgNP-Bo also demonstrated excellent performance for Paracetamol detection in synthetic combinations including Tyrosine, Alanine, and Leucine. The suggested technique applied effectively for the quantitative analysis of synthetic mixtures, which makes it possible to employ Ag NPs going forward to determine biological molecules when interfering analytes from actual samples are present. Keywords: Silver nanoparticles; Brassica oleracea; Paracetamol; 2nd order derivative spectrophotometry; Interferences.

Monophenolase assay using excitation-emission matrix fluorescence and ELMAN neural network assisted by whale optimization algorithm

Tyrosinase plays a vital role for melanogenesis and inherently involves both monophenolase activity and diphenolase activity. Monophenolase catalyzes hydroxylation of tyrosine to l-DOPA (L-3,4-dihydroxyphenylalanine). Real-time monophenolase assay method is of outstanding interest for both scientific research and industrial application. A combined strategy of three-dimensional excitation-emission matrix (EEM) fluorescence spectra and artificial neural network was developed to determine monophenolase activity. A quantitation system for tyrosine in presence of l-DOPA was designed based on ELMAN neural network. Principal component analysis (PCA) was conducted to reduce the dimensionality of fluorescence spectra. Four principal components was used as input variables. Whale optimization algorithm (WOA) was implemented to optimize the initial weights and threshold network. Real-time concentration of tyrosine in monophenolase reaction was monitored to calculate the initial velocity for tyrosine consumption. The exclusive monophenolase activity without interference from diphenolase reaction was determined. Limit of detection (LOD) for monophenolase assay is 0.0113 U mL−1. Using the proposed method, enzyme kinetics for monophenolase was investigate. Km was calculated as 14.16 μM. Inhibitor for monophenolase was screened by using model molecule kojic acid with IC50 of 3.49 μM. The assay method exhibited a promising prospect to characterize the kinetics and inhibitor of monophenolase.

A suicide diiron oxygenase in p‐aminobenzoate biosynthesis in Chlamydia trachomatis

Folate is an essential one‐carbon carrier cofactor required for essential biological reactions such as amino acid and DNA biosynthesis. Folates are comprised of three chemical moieties: a pteridine ring, p‐aminobenzoate (pABA), and glutamate residues. Chlamydia trachomatis has been shown to synthesize folate de novo; however, it is missing several genes involved in the canonical folate biosynthesis pathway. Previous work has demonstrated that a single gene, ct610, functionally replaces the enzymes responsible for pABA production in the canonical biosynthesis pathway. However, CT610 does not use chorismate as the precursor to pABA as is used in the canonical pathway. Further experiments showed that isotopically labeled tyrosine was incorporated into the pABA molecule when synthesized by CT610 in vivo. However, in vitro experiments demonstrated that CT610 produces pABA in the presence of oxygen and a reducing agent without any added substrates, including tyrosine. This led to the hypothesis that CT610 is a self‐sacrificing “suicide” enzyme that donates an active site tyrosine residue in synthesizing pABA. CT610 has low sequence similarity to non‐heme diiron monooxygenases such as methane monooxygenase and class Ia ribonucleotide reductase, and the previously solved crystal structure of CT610 revealed a diiron active site. Here we describe our recent progress towards understanding this unique suicide mechanism for pABA biosynthesis. To determine the tyrosine residue sacrificed in the reaction, we generated five active site tyrosine to phenylalanine mutants and found that two of the variants completely abolished pABA production, suggesting that one of these residues is the precursor to pABA. Further, a conserved lysine residue is also essential for the reaction and may be a sacrificial amino group donor. We have confirmed the oxygenase activity of wild‐type CT610, which requires only a reducing agent and is not stimulated by the presence of tyrosine or other possible substrates. Further, we developed an Fe(II) reconstitution procedure, where the reconstituted enzyme exhibits a drastic increase in oxygenase activity. However, surprisingly, the reconstituted enzyme does not exhibit increased pABA synthase activity, although EDTA treatment of the as‐purified enzyme almost completely inhibits pABA production. This suggests that a metal other than iron is required for the reaction and thus current work is focused on testing other potential metal cofactors that may play a role in the novel suicide reaction.

Tyrosine as a novel potential stabilizer in an electroless Ni-P bath exempt of trisodium citrate as complexing agent: Chemical baths optimization and comparative study

• New formulation of Ni-P alloy electroless plating baths using hypophosphite as reducing agent. • Abundance of trisodium citrate as the main component acting as a complexing agent in Ni-P electroless plating baths. • Addition of tyrosine as a complexing-stabilizing agent led to a significant improvement in bath stability accompanied by a deposition rate of 18 µm h −1 . • Optimization of the tyrosine-containing bath led to a gain of 67% NiSO4,6H2O and 85% CH 3 COONH 4 . The effect of tyrosine (C 9 H 11 NO 3 ) as a new stabilizing agent on the composition and conditions of the electroless plating bath of the Ni-P alloy was studied. A comparative study with trisodium citrate, which is commonly used, as a stabilizing complexing agent revealed the effect of tyrosine in this study. Scanning electron microscopy (SEM) and X-Ray Energy Dispersion (EDX) are used to study the properties of the Ni-P coating deposit developed in the presence of tyrosine and trisodium citrate. The result of this optimization showed that the use of tyrosine causes the concentration of NiSO 4 and CH 3 COONH 4 in the bath to decrease to 67% and 85%, respectively. In contrast, the use of trisodium citrate had no effect neither on the composition nor on the effect of the bath conditions of the deposit. In addition, the use of C 9 H 11 NO 3 as a stabilizing agent in the bath promotes the increase of the phosphorus content more than trisodium citrate when optimizing the accelerating agent in the bath and therefore changes the structure of the Ni-P deposits developed.

Coconut Carbon Dots: Progressive Large-Scale Synthesis, Detailed Biological Activities and Smart Sensing Aptitudes towards Tyrosine.

In the recent era, carbon dots (C-dots) have been extensively considered as a potential tool in drug delivery analysis. However, there have been fewer reports in the literature on their application in the sensing of amino acids. As part of our ongoing research on coconut-husk-derived C-dots, we synthesized C-dots under different temperature conditions and utilized them in the field of amino acid sensing and found them to be highly selective and sensitive towards tyrosine. The detailed characterization of the prepared C-dots was carried out. The developed C-dots exhibit good values of quantum yield. BSA, HSA and glutamic acid were utilized to explore the binding efficiency of C-dots with biologically active components. Hemolysis, blood clotting index activity and cell viability assays using the prepared C-dots were evaluated and they were found to be biocompatible. Therefore, the C-dots described in this work have high potential to be utilized in the field of amino acid sensing, especially L-tyrosine. The limit of detection and the binding constant for the developed C-dots in the presence of tyrosine were found to be 0.96 nM and 296.38 nM−1, respectively. The efficiency of the developed C-dots was also investigated in the presence of various other amino acids and different water mediums in order to enhance the working scope of the developed sensors.

Pheomelanin Effect on UVB Radiation-Induced Oxidation/Nitration of l-Tyrosine.

Pheomelanin is a natural yellow-reddish sulfur-containing pigment derived from tyrosinase-catalyzed oxidation of tyrosine in presence of cysteine. Generally, the formation of melanin pigments is a protective response against the damaging effects of UV radiation in skin. However, pheomelanin, like other photosensitizing substances, can trigger, following exposure to UV radiation, photochemical reactions capable of modifying and damaging cellular components. The photoproperties of this natural pigment have been studied by analyzing pheomelanin effect on oxidation/nitration of tyrosine induced by UVB radiation at different pH values and in presence of iron ions. Photoproperties of pheomelanin can be modulated by various experimental conditions, ranging from the photoprotection to the triggering of potentially damaging photochemical reactions. The study of the photomodification of l-Tyrosine in the presence of the natural pigment pheomelanin has a special relevance, since this tyrosine oxidation/nitration pathway can potentially occur in vivo in tissues exposed to sunlight and play a role in the mechanisms of tissue damage induced by UV radiation.

Characterization of the TyrR Regulon in the Rhizobacterium Enterobacter ludwigii UW5 Reveals Overlap with the CpxR Envelope Stress Response.

The TyrR transcription factor controls the expression of genes for the uptake and biosynthesis of aromatic amino acids in Escherichia coli In the plant-associated and clinically significant proteobacterium Enterobacter ludwigii UW5, the TyrR orthologue was previously shown to regulate genes that encode enzymes for synthesis of the plant hormone indole-3-acetic acid and for gluconeogenesis, indicating a broader function for the transcription factor. This study aimed to delineate the TyrR regulon of E. ludwigii by comparing the transcriptomes of the wild type and a tyrR deletion strain. In E. ludwigii, TyrR positively or negatively regulates the expression of over 150 genes. TyrR downregulated expression of envelope stress response regulators CpxR and CpxP through interaction with a DNA binding site in the intergenic region between divergently transcribed cpxP and cpxR Repression of cpxP was alleviated by tyrosine. Methyltransferase gene dmpM, which is possibly involved in antibiotic synthesis, was strongly activated in the presence of tyrosine and phenylalanine by TyrR binding to its promoter region. TyrR also regulated expression of genes for aromatic catabolism and anaerobic respiration. Our findings suggest that the E. ludwigii TyrR regulon has diverged from that of E. coli to include genes for survival in the diverse environments that this bacterium inhabits and illustrate the expansion and plasticity of transcription factor regulons.IMPORTANCE Genome-wide RNA sequencing revealed a broader regulatory role for the TyrR transcription factor in the ecologically versatile bacterium Enterobacter ludwigii beyond that of aromatic amino acid synthesis and transport that constitute the role of the TyrR regulon of E. coli In E. ludwigii, a plant symbiont and human gut commensal, the TyrR regulon is expanded to include genes that are beneficial for plant interactions and response to stresses. Identification of the genes regulated by TyrR provides insight into the mechanisms by which the bacterium adapts to its environment.

Development of multifunctional Cu sensitized Ag-dextran nanocomposite for selective and sensitive detection of mercury from environmental sample and evaluation of its photocatalytic and anti-microbial applications

Mercury has been considered as the most toxic metal pollutants that pose lethal threat to environment and the human health at small concentrations. Thus, the development of a rapid, inexpensive and simple technique for Hg2+ ion detection in real aqueous samples is paramount. The present study reported a colorimetric assay for sensing Hg2+ ion using Cu sensitized Ag-dextran nanocomposite (NCs) in presence of tyrosine. The particle was characterized by UV–visible (vis) spectrophotometer, zeta sizer, HR-TEM, particle size analyzer, FT-IR, EDAX and XRD. The NCs possessed a hydrodynamic diameter of 26 ± 1.4 nm and − 32.21 ± 3 mV was the zetapotential value. The colour of Ag/Cu NCs was brownish yellow due to the LSPR band centred at 408 nm. An appreciable colour change was observed from yellowish brown to colourless after interaction with Hg2+ ion. A good linearity existed in the correlation curve between the absorbance value (ℷ = 408 nm) and the Hg2+ ion concentrations (20 nM – 100 nM). A simple, low cost paper-strip based sensor of Ag/Cu NCs used as an real time portable Hg2+ detection. The influence of other metal ions, pH (5.0 to 9.0), salinity (0.1–0.8%) and temperature (15–50 °C) for the Hg2+ detection was also investigated. The NCs exhibits high specificity, sensitivity and stability towards the Hg2+ detection at low nano molar level. Additionally, the NCs exhibited excellent MB degradation under irradiation of visible light and it also showed antimicrobial activity against B. subtilis and E. coli. The study demonstrated the application of Cu sensitized Ag-dextran NCs in detection, photocatalysis, and as an antimicrobial agent.

Simultaneous and selective determination of dopamine and tyrosine in the presence of uric acid with 2D-MoS2 nanosheets modified screen-printed carbon electrodes

Two-dimensional molybdenum disulphide nanosheets (2D-MoS2) were prepared by liquid-phase exfoliation and used to modify screen-printed carbon electrodes (SPCE), in order to develop an electrochemical sensor for the simultaneous determination of dopamine (DA) and tyrosine (Tyr) in presence of uric acid (UA). To demonstrate the layered morphology, the synthesized molybdenum disulphide nanostructures, have been characterized by Raman and SEM in both liquid dispersion and after deposition on SPCE. The performances of the 2D-MoS2-SPCE electrode have been tested and optimized in terms of sensitivity, reaching high sensitivity values of 1044 μA mM−1 cm−2 for DA and 321 μA mM−1 cm−2 for Tyr, selectivity against UA and high stability. The simultaneous detection of these biomolecules is the first study so far reported with the use of 2D-MoS2-based sensors. The promising characteristics of the developed electrodes suggest 2D-MoS2 as a versatile, low cost and easy to produce material for the next generation of electrochemical sensors of a variety of important biomolecules.

Rapid colorimetric and spectroscopy based sensing of mercury by surface functionalized silver nanoparticles in the presence of tyrosine

Heavy metals are considered as the major environmental pollutant and it reached through mining and industrial waste water, among which mercury is the most toxic heavy metal. The current study reports on Hg2+ detection by using 3-(Trimethoxysilyl) propyl methacrylate (TMPM) functionalized silver nanoparticles (Ag NPs). The prepared Ag NPs was characterized by UV–visible spectrophotometer, particle size analyser, emission-dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), and zeta sizer. UV–visible spectrophotometer study of Ag NPs showed λmax at 404 nm. The average diameter of the particles was found to be 10 ± 1.4 nm and it possessed a zeta potential of −34.32 ± 3 mV. The Hg2+ detection by Ag NPs was observed in the variation in colour from pale yellow to colourless. The peak disappearance was observed in UV–visible spectrophotometer absorption spectra after addition of Hg2+ and measurements of particle size and surface charge of Ag NPs confirmed the aggregation. The detection of Hg2+ by the probe was not interfered by other metal ions in the test solution. The paper and gel-based methods were also developed to detect the Hg2+ from aqueous sample. A linear relationship of y = 0.0007x − 0.0081, R2=0.9816 was obtained between the plot of concentration of Hg2+ ion and the absorbance of Ag NPs on quantification of mercury. The amount of mercury present in the aqueous sample collected from Bhavani River was estimated to be 62.3 ± 1.9 nM which was further confirmed with atomic absorption spectrophotometric analysis. The study found that the prepared probe is highly responsive and specific towards the Hg2+ detection at nano molar level. Hence, the probe is a great tool for effective detection and estimation of Hg2+ from various environmental samples.

A Carbon Paste Electrode Modified by Graphene Oxide/Fe3O4@SiO2/Ionic Liquid Nanocomposite for Voltammetric Determination of Acetaminophen in the Presence of Tyrosine

Herein, we introduce a novel modification process for carbon paste electrode by magnetic core–shell nanocomposite of graphene oxide/Fe3O4@SiO2 and n-hexyl-3-methylimidazolium hexafluoro phosphate as ionic liquid. Electrochemical features of this modified carbon paste electrode and its performance evaluation in simultaneous detection of acetaminophen and tyrosine via voltammetric oxidation was investigated. Moreover, diagnostic techniques including cyclic voltammetry, square wave voltammetry and chronoamperometry were applied in order to study the electrochemical oxidation behavior of this sensor toward acetaminophen. According to square wave voltammetry results, linear dynamic range between 1.0 × 10–6–1.0 × 10–3 M was observed for acetaminophen. The function of modified electrode in real samples containing acetaminophen and tyrosine was satisfactory.

1H-NMR-based metabolomics to investigate the effects of Phoenix dactylifera seed extracts in LPS-IFN-γ-induced RAW 264.7 cells.

Inflammation has been revealed to play a central role in the onset and progression of many illnesses. Nuclear magnetic resonance (NMR) based metabolomics method was adopted to evaluate the effects of Phoenix dactylifera seeds, in particular the Algerian date variety of Deglet on the metabolome of the LPS-IFN-γ-induced RAW 264.7 cells. Variations in the extracellular and intracellular profiles emphasized the differences in the presence of tyrosine, phenylalanine, alanine, proline, asparagine, isocitrate, inosine and lysine. Principal component analysis (PCA) revealed noticeable clustering patterns between the treated and induced RAW cells based on the metabolic profile of the extracellular metabolites. However, the effects of treatment on the intracellular metabolites appears to be less distinct as suggested by the PCA and heatmap analyses. A clear group segregation was observed for the intracellular metabolites from the treated and induced cells based on the orthogonal partial least squares-discriminant analysis (OPLS-DA) score plot. Likewise, 11 of the metabolites in the treated cells were significantly different from those in the induced groups, including amino acids and succinate. The enrichment analysis demonstrated that treatment with Deglet seed extracts interfered with the energy and of amino acids metabolism. Overall, the obtained data reinforced the possible application of Deglet seeds as a functional food with anti-inflammatory properties.

Phosphorylated tyrosine 93 of hepatitis C virus nonstructural protein 5A is essential for interaction with host c-Src and efficient viral replication

The hepatitis C virus (HCV) nonstructural protein 5A (NS5A) plays a key role in viral replication and virion assembly, and the regulation of the assembly process critically depends on phosphorylation of both serine and threonine residues in NS5A. We previously identified SRC proto-oncogene, nonreceptor tyrosine kinase (c-Src), as an essential host component of the HCV replication complex consisting of NS5A, the RNA-dependent RNA polymerase NS5B, and c-Src. Pulldown assays revealed an interaction between NS5A and the Src homology 2 (SH2) domain of c-Src; however, the precise binding mode remains undefined. In this study, using a variety of biochemical and biophysical techniques, along with molecular dynamics simulations, we demonstrate that the interaction between NS5A and the c-Src SH2 domain strictly depends on an intact phosphotyrosine-binding competent SH2 domain and on tyrosine phosphorylation within NS5A. Detailed analysis of c-Src SH2 domain binding to a panel of phosphorylation-deficient NS5A variants revealed that phosphorylation of Tyr-93 located within domain 1 of NS5A, but not of any other tyrosine residue, is crucial for complex formation. In line with these findings, effective replication of subgenomic HCV replicons as well as production of infectious virus particles in mammalian cell culture models were clearly dependent on the presence of tyrosine at position 93 of NS5A. These findings indicate that phosphorylated Tyr-93 in NS5A plays an important role during viral replication by facilitating NS5A's interaction with the SH2 domain of c-Src.

Gut bacterial tyrosine decarboxylases restrict levels of levodopa in the treatment of Parkinson\u2019s disease

Human gut microbiota senses its environment and responds by releasing metabolites, some of which are key regulators of human health and disease. In this study, we characterize gut-associated bacteria in their ability to decarboxylate levodopa to dopamine via tyrosine decarboxylases. Bacterial tyrosine decarboxylases efficiently convert levodopa to dopamine, even in the presence of tyrosine, a competitive substrate, or inhibitors of human decarboxylase. In situ levels of levodopa are compromised by high abundance of gut bacterial tyrosine decarboxylase in patients with Parkinson’s disease. Finally, the higher relative abundance of bacterial tyrosine decarboxylases at the site of levodopa absorption, proximal small intestine, had a significant impact on levels of levodopa in the plasma of rats. Our results highlight the role of microbial metabolism in drug availability, and specifically, that abundance of bacterial tyrosine decarboxylase in the proximal small intestine can explain the increased dosage regimen of levodopa treatment in Parkinson’s disease patients.

Pottasium triiodide enhanced turn-off sensing of tyrosine in carbon dot platform

In this work, a turn-off sensing approach for simple and sensitive determination of tyrosine is developed on the basis of quenching of fluorescence of carbon dot. When carbon dot is mixed with potassium triiodide, the fluorescence of carbon dot undergo quenching and this quenching phenomena get enhanced in the presence of tyrosine. The possible interfering amino acids and biomolecules exhibit turn-on behaviour and thus tyrosine has good selectivity. The limit of detection of tyrosine is 950 nM. Real sample analysis in serum sample shows good recovery percentage.

Tyrosinase-mediated Peptide Conjugation with Chitosan-coated Gold Nanoparticles.

The conjugation of biomolecules, such as protein, sugar, and DNA, with metal nanoparticles is an important technique for bioassay and biomaterial preparation. In this study, we aim to enzymatically immobilize a functional peptide on gold nanoparticles (AuNPs) using a single-step reaction. We used tyrosinase, a catechol oxidase, to immobilize an enzymatic peptide. We performed immobilization experiments of a fluorescent compound-linked caspase-3 substrate peptide using tyrosinase on chitosan-coated AuNPs. Peptides were effectively immobilized onto the AuNPs depending on the presence of tyrosine within the sequence, which suggests the DOPA-quinone produced from tyrosine, via tyrosinase, is connected to the chitosan amino group. Although fluorescent emission from the immobilized capase-3 substrate was quenched by AuNPs, fluorescence intensity recovery occurred due to the addition of caspase-3. Thus, we were able to easily prepare functional AuNPs that can be used for a caspase-3 activity assay. Our results indicate that the tyrosinase-mediated peptide link to chitosan-coated particles is a useful technique for preparing functionalized nanoparticles.

Voltammetric determination of dopamine in the presence of tyrosine using graphite screen-printed electrode modified with graphene quantum dots

Dopamine (DA) is an important neurotransmitter that belongs to the catecholamine group and plays a very significant role in the central nervous, renal, hormonal, and cardiovascular systems. As a result, dysfunction of the dopaminergic system in the central nervous system (CNS) has been related to neurological disorders such as schizophrenia and Parkinson’s disease. Therefore, in this work, a screen-printed electrode was modified by graphene quantum dots (GQD/SPE) in order to be used as sensor for dopamine in the presence of tyrosine. To evaluate the efficiency of the developed electrode toward detection of dopamine and tyrosine in aqueous solutions, various electrochemical methods including cyclic voltammetry (CV), chronoamperometry (CHA), and differential pulse voltammetry (DPV) techniques were employed. Application of GQD/SPE created a separation of 435 mV in the oxidation peak potentials of dopamine and tyrosine. The calibration curves were within the range of 0.1–1000.0 and 1.0–900.0 μM for dopamine and tyrosine, respectively. The detection limits (S/N = 3) were determined as 0.05 and 0.5 μM for dopamine and tyrosine, respectively. The diffusion coefficients using chronoamperometry at the surface of modified electrode were determined as 9.0 × 10−5 and 6.4 × 10−5 cm2 s−1 for dopamine and tyrosine, respectively.

СПЕКТРОФОТОМЕТРИЧЕСКОЕ ОПРЕДЕЛЕНИЕ L-ТИРОЗИНА В НАНОКОНСТРУКЦИЯХ НА ОСНОВЕ СУБЪЕДИНИЦ ВИРУСА ГРИППА B/FLORIDA/04/2006 И БИОРАЗЛАГАЕМОГО ПОЛИМЕРА ДЕКСТРАНА

Our aim was to synthesize antigen polysaccharide complexes based on the surface subunits of the influenza virus B/Florida/04/2006 in the presence of various primary amines and to study their physicochemical properties. The antigen polysaccharide complexes were synthesized by conjugation with a partially oxidized dextran and subsequent reduction by natrium borane. The biological and physicochemical properties of the as-synthesized antigen polysaccharide nanoscale constructions are investigated. On the basis of the results, we have proposed a spectrophotometric method for determining tyrosine in antigen samples modified by oxidized dextran in the presence of tyrosine. Ratios between the main components of the synthesized antigen polysaccharide nanoscale constructions loaded with an additional amount of tyrosine have been determined. It is shown that the synthesized antigen polysaccharide complexes contain 16-30 parts of dextran and 40-130 parts of additionally taken amino acid residues per 1 part of antigens. Approximate molecular weights of the synthesized conjugates are shown to range from 1 to 2 million Da. Nanoscale constructions with such molecular weights are comparable with those of viral particles and, in fact, can be considered as virus-like particles.