Tryptophan Oxidation Research Articles

Tryptophan Oxidation of a Monoclonal Antibody Under Diverse Oxidative Stress Conditions: Distinct Oxidative Pathways Favor Specific Tryptophan Residues.

Tryptophan oxidation can play an important role in selecting therapeutic monoclonal antibodies for commercialization. Monoclonal antibodies that harbor particularly sensitive tryptophan residues are typically discarded in favor of oxidation resistant antibodies. The susceptibility of any individual tryptophan residue to oxidation is typically evaluated through forced degradation studies during the molecule development process. We compared the results of several common forced degradation "stress tests" for each tryptophan residue in a monoclonal antibody and found that high-stress oxidation conditions consistently provide a different ranking of oxidative sensitivity across the individual tryptophan residues compared to long-term thermal stability or low-stress conditions. We subsequently determined that this difference in ranking is largely due to an overabundance of double oxidation (i.e. detected as+32Da) of specific tryptophan residues under high stress conditions compared to single oxidation (i.e.+16Da). We posit that this double oxidation is in fact mechanistically distinct from the observed single oxidation and that high stress conditions favor the double oxidation mechanism (and double oxidation sensitive tryptophan residues) while single oxidation appears to be the primary mode of oxidation under H2O2 stress and long-term thermal stability and favors different tryptophan residues which are more susceptible to the single oxidation mechanism.

Hepatocyte-intrinsic type I interferon signaling reprograms metabolism and reveals a novel compensatory mechanism of the tryptophan-kynurenine pathway in viral hepatitis.

The liver is a central regulator of metabolic homeostasis and serum metabolite levels. Hepatocytes are the functional units of the liver parenchyma and not only responsible for turnover of biomolecules but also act as central immune signaling platforms. Hepatotropic viruses infect liver tissue, resulting in inflammatory responses, tissue damage and hepatitis. Combining well-established in vitro and in vivo model systems with transcriptomic analyses, we show that type I interferon signaling initiates a robust antiviral immune response in hepatocytes. Strikingly, we also identify IFN-I as both, sufficient and necessary, to induce wide-spread metabolic reprogramming in hepatocytes. IFN-I specifically rewired tryptophan metabolism and induced hepatic tryptophan oxidation to kynurenine via Tdo2, correlating with altered concentrations of serum metabolites upon viral infection. Infected Tdo2-deficient animals displayed elevated serum levels of tryptophan and, unexpectedly, also vast increases in the downstream immune-suppressive metabolite kynurenine. Thus, Tdo2-deficiency did not result in altered serum homeostasis of the tryptophan to kynurenine ratio during infection, which seemed to be independent of hepatocyte-intrinsic compensation via the IDO-axis. These data highlight that inflammation-induced reprogramming of systemic tryptophan metabolism is tightly regulated in viral hepatitis.

A voltammetric sensor for simultaneous determination of tryptophan and 5-hydroxytryptophan

The present work proposes a method for simultaneous determination of tryptophan and 5-hydroxytryptophan on the carbon-bearing electrode modified with multiwall carbon nanotubes and polyfolic acid. Analytical signals are conditioned by oxidation of tryptophan and 5–hydroxytryptophan from the complex containing polyfolic acid. Preparation of the electrode consists in the formation of the B9 vitamin film on the surface of the carbon-bearing electrode, modified with multiwall carbon nanotubes by the method of cyclic voltammetry. The detection limit of tryptophan and 5-hydroxytryptophan is 1 × 10–7 M.

RPTMDetermine: A Fully Automated Methodology for Endogenous Tyrosine Nitration Validation, Site-Localization, and Beyond.

We present herein rPTMDetermine, an adaptive and fully automated methodology for validation of the identification of rarely occurring post-translational modifications (PTMs), using a semisupervised approach with a linear discriminant analysis (LDA) algorithm. With this strategy, verification is enhanced through similarity scoring of tandem mass spectrometry (MS/MS) comparisons between modified peptides and their unmodified analogues. We applied rPTMDetermine to (1) perform fully automated validation steps for modified peptides identified from an in silico database and (2) retrieve potential yet-to-be-identified modified peptides from raw data (that had been missed through conventional database searches). In part (1), 99 of 125 3-nitrotyrosyl-containing (nitrated) peptides obtained from a ProteinPilot search were validated and localized. Twenty nitrated peptides were falsely assigned because of incorrect monoisotopic peak assignments, leading to erroneous identification of deamidation and nitration. Five additional nitrated peptides were, however, validated after performing nonmonoisotopic peak correction. In part (2), an additional 236 unique nitrated peptides were retrieved and localized, containing 113 previously unreported nitration sites; 25 endogenous nitrated peptides with novel sites were selected and verified by comparison with synthetic analogues. In summary, we identified and confidently validated 296 unique nitrated peptides-collectively representing the largest number of endogenously identified 3-nitrotyrosyl-containing peptides from the cerebral cortex proteome of a Macaca fascicularis model of stroke. Furthermore, we harnessed the rPTMDetermine strategy to complement conventional database searching and enhance the confidence of assigning rarely occurring PTMs, while recovering many missed peptides. In a final demonstration, we successfully extended the application of rPTMDetermine to peptides featuring tryptophan oxidation.

Elucidation of molecular interactions between human γD-crystallin and quercetin, an inhibitor against tryptophan oxidation

Different post-translational changes in eye lens crystallin proteins contribute towards the development of cataract. We have studied in vitro oxidative modification of tryptophan (Trp) residues of human γD-crystallin (HGD) towards formation of N-formylkynurenine (NFK) associated with cataractogenesis. This oxidation was found to be inhibited by quercetin at relatively low concentration. Interactions between quercetin and HGD were further studied using fluorescence techniques. Binding and quenching constants were determined as ∼104 M −1. Static quenching of fluorescence due to HGD–quercetin complex formation at ground state was confirmed by finding excited state life time of Trp residues. Energy transfer occurred between the protein and quercetin. Hydrogen bonding and/or van der Waals interactions were involved between HGD and quercetin. Synchronous and three-dimensional fluorescence along with far-UV CD studies suggested no major conformational alterations occurred in HGD due to quercetin binding. Experimental observations were supported by the docking results. Communicated by Ramaswamy H. Sarma

A40 INTESTINAL EPITHELIAL NCOR1 TARGETS TRYPTOPHAN METABOLISM AND PROTECTS AGAINST EXPERIMENTAL COLITIS

Abstract Background The nuclear co-repressor NCOR1 is a central protein that orchestrates the assembly of a large transcriptional repression complex. NCOR1 controls activation of macrophages by repressing a large variety of pro-inflammatory genes. Aims We aimed to investigate the role of intestinal epithelial NCOR1 during experimental colitis. Methods Conditional deletion of Ncor1 in the whole intestinal epithelium was achieved by crossing Villin-Cre and Ncor1loxP/loxP C57BL/6 mouse models. A gene profiling analysis in the colon of non-diseased NCOR1ΔIEC and control mice was performed. NCOR1ΔIEC and control littermate mice were treated with dextran sulfate sodium (DSS) in drinking water. Results DSS-induced colitis in NCOR1ΔIEC mice was more severe than control mice according to survival as well as clinical observations. A statistical analysis predicted 85 unique and mapped transcripts being significantly modulated between NCOR1ΔIEC and control mice. An Ingenuity Pathway Analysis from these predicted target genes identified gastrointestinal disease (79 transcripts) as top disease and biofunction. Analysis of enriched targets in specific canonical pathways predicted an increase in the tryptophan degradation pathway (P = 3.2E-02), a pathway recently demonstrated to be strongly relevant to inflammatory bowel disease severity. Indoleamine-pyrrole 2,3-dioxygenase (IDO1), that catalyzes the first and rate-limiting step of tryptophan oxidation, was induced more than 7 times in the colon of NCOR1ΔIEC mice. Induction of Ido1 was also confirmed in cultured ex vivo colon organoids deleted for Ncor1. Conclusions Our results highlight the critical role of NCOR1 to maintain intestinal inflammatory homeostasis during experimental colitis and uncover a novel function for NCOR1 in the regulation of Ido1 expression and potentially tryptophan metabolism. Funding Agencies CIHR

Picolinic acid, a tryptophan oxidation product, does not impact bone mineral density but increases marrow adiposity.

Tryptophan is an essential amino acid catabolized initially to kynurenine (kyn), an immunomodulatory metabolite that we have previously shown to promote bone loss. Kyn levels increase with aging and have also been associated with neurodegenerative disorders. Picolinic acid (PA) is another tryptophan metabolite downstream of kyn. However, in contrast to kyn, PA is reported to be neuroprotective and further, to promote osteogenesis in vitro. Thus, we hypothesized that PA might be osteoprotective in vivo. In an IACUC-approved protocol, we fed PA to aged (23-month-old) C57BL/6 mice for eight weeks. In an effort to determine potential interactions of PA with dietary protein we also fed PA in a low-protein diet (8%). The mice were divided into four groups: Control (18% dietary protein), +PA (700ppm); Low-protein (8%), +PA (700ppm). The PA feedings had no impact on mouse weight, body composition or bone density. At sacrifice bone and stem cells were collected for analysis, including μCT and RT-qPCR. Addition of PA to the diet had no impact on trabecular bone parameters. However, marrow adiposity was significantly increased in PA-fed mice, and in bone marrow stromal cells isolated from these mice increases in the expression of the lipid storage genes, Plin1 and Cidec, were observed. Thus, as a downstream metabolite of kyn, PA no longer showed kyn's detrimental effects on bone but instead appears to impact energy balance.

Caveolin proteins electrochemical oxidation and interaction with cholesterol

Caveolae consist in lipid raft domains composed of caveolin proteins, cholesterol, glycosphingolipids, and GPI-anchored proteins. Caveolin proteins present three different types, caveolin 1 (CAV-1), caveolin 2 (CAV-2) and caveolin 3 (CAV-3), with a very similar structure and amino acid composition. The native caveolin proteins oxidation mechanism was investigated for the first time, at a glassy carbon electrode, using cyclic, square wave and differential pulse voltammetry. The three native caveolin proteins oxidation mechanism presented only one tyrosine and tryptophan amino acid residues oxidation peak. Denatured caveolin proteins presented also the tyrosine, tryptophan and cysteine amino acid residues oxidation peaks. The reverse cholesterol transport is related to caveolae and caveolin proteins, and CAV-1 is directly connected to cholesterol transport. The influence of cholesterol on the three caveolin proteins electrochemical behaviour was evaluated. In the absence and in the presence of cholesterol, significant differences in the CAV-1 oxidation peak current were observed.

A novel nanocomposite electrochemical sensor based on green synthesis of reduced graphene oxide/gold nanoparticles modified screen printed electrode for determination of tryptophan using response surface methodology approach

In this study, a new method is presented for the direct determination of L-tryptophan (Try), using E. tereticornis leave as an environmentally friendly reducing agent for synthesis of reduced graphene oxide/gold nanoparticles (rGO/AuNPs). Scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy analyses showed a uniform distribution of gold nanoparticles on thin layers of reduced graphene oxide. The synthesized nanocomposite was used as a sensitive and electroactive substrate on the surface of screen-printed electrode for electrochemical oxidation of Try in biological samples. Differential pulse voltammetry (DPV) and cyclic voltammetry (CV) showed a reliable analytical signal for the oxidation of Tryptophan at 0.65 V. Response surface methodology (RSM) model was utilized for improving the sensitivity of detection based on central composite design. Under the optimum conditions (Britton Robinson buffer, pH: 6.0; AuNPs/rGO ratio (W/W): 4 and drop casted nanocomposite volume: 5 µl), the calibration curve of Try is linear between 0.5–500 µmol/L (R = 0.9976) with detection limit (LOD) and limit of quantification (LOQ) of 0.39 and 1.32 µmol/L, respectively. In addition, the SPE/rGO/AuNPs electrochemical sensor showed good reproducibility, high sensitivity and good selectivity towards the determination of Try, which makes it suitable for the analysis of Try in human plasma, serum and saliva.

Untargeted Proteomics-Based Profiling for the Identification of Novel Processing-Induced Protein Modifications in Milk.

Nonenzymatic post-translational protein modifications (nePTMs) affect the nutritional, physiological, and technological properties of proteins in food and in vivo. In contrast to the usual targeted analyses, the present study determined nePTMs in processed milk in a truly untargeted proteomic approach. Thus, it was possible to determine to which extent known nePTM structures explain protein modifications in processed milk and to detect and identify novel products. The method combined ultrahigh-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry with bioinformatic data analysis by the software XCMS. The nePTMs detected by untargeted profiling of a β-lactoglobulin-lactose model were incorporated in a sensitive scheduled multiple reaction monitoring method to analyze these modifications in milk samples and to monitor their reaction kinetics during thermal treatment. Additionally, we identified the structures of unknown modifications. Lactosylation, carboxymethylation, formylation of lysine and N-terminus, glycation of arginine, oxidation of methionine, tryptophan, and cysteine, oxidative deamination of N-terminus, and deamidation of asparagine and glutamine were the most important reactions of β-lactoglobulin during milk processing. The isomerization of aspartic acid was observed for the first time in milk products, and N-terminal 4-imidazolidinone was identified as a novel nePTM.

M. leprae HSP18 suppresses copper (II) mediated ROS generation: Effect of redox stress on its structure and function

Mycobacterium leprae, causative organism of leprosy, is known to counter redox stress generated by reactive oxygen species (ROS) during its survival inside host macrophages. But, the involvement of any antigenic protein(s) for countering such redox stress is still unknown. Interestingly, M. leprae HSP18, an important antigenic protein that helps in the growth and survival of M. leprae pathogen inside host macrophages, is induced under redox stress. Moreover, HSP18 also interacts with Cu2+. Copper (II) can induce redox stress via Fenton reaction. But, whether HSP18 suppresses Cu2+ mediated ROS generation, is still far from clear. Also, the effect of redox stress on its structure and function is not known. In this study, we show that HSP18 efficiently suppresses Cu2+ mediated generation of ROS and also prevents the redox mediated aggregation of a client protein (γD-crystallin). Upon exposure to substantial redox stress, irreversible perturbation in the secondary and tertiary structure of HSP18 and the tryptophan and tyrosine oxidation are evidenced. Interestingly, HSP18 retains a considerable amount of functionality even after being exposed to substantial redox stress. Perhaps, the redox scavenging ability as well as the chaperone function of HSP18 may possibly help M. leprae pathogen to counter redox stress inside host macrophages.

Modeling Tryptophan/Indoleamine 2,3-Dioxygenase with Heme Superoxide Mimics: Is Ferryl the Key Intermediate?

Tryptophan oxidation in biology has been recently implicated in a vast array of paramount pathogenic conditions in humans, including multiple sclerosis, rheumatoid arthritis, type-I diabetes, and cancer. This 2,3-dioxygenative cleavage of the indole ring of tryptophan with dioxygen is mediated by two heme enzymes, tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO), during its conversion to N-formylkynurenine in the first and rate-limiting step of kynurenine pathway. Despite the pivotal significance of this enzymatic transformation, a vivid viewpoint of the precise mechanistic events is far from complete. A heme superoxide adduct is thought to be the active oxidant in both TDO and IDO, which, following O-O bond cleavage, presumably generates a key ferryl (FeIV=O) reaction intermediate. This study, for the first time in model chemistry, demonstrates the potential of synthetic heme superoxide adducts to mimic the bioinorganic chemistry of indole dioxygenation by TDO and IDO, challenging the widely accepted categorization of these metal adducts as weak oxidants. Herein, an electronically divergent series of ferric heme superoxo oxidants mediates the facile conversion of an array of indole substrates into their corresponding 2,3-dioxygenated products, while shedding light on an unequivocally occurring, putative ferryl intermediate. The oxygenated indole products have been isolated in ∼31% yield, and characterized by LC-MS, 1H and 13C NMR, and FT-IR methodologies, as well as by 18O2(g) labeling experiments. Distinctly, the most electron-deficient superoxo adduct is observed to react the fastest, specifically with the most electron-rich indole substrate, underscoring the cruciality of electrophilicity of the heme superoxide moiety in facilitating the initial indole activation step. Comprehensive understanding of such mechanistic subtleties will benefit future attempts in the rational design of salient therapeutic agents, including next generation anticancer drug targets with amplified effectivity.

Hypoxia Inducible Factor 1α Inhibits the Expression of Immunosuppressive Tryptophan-2,3-Dioxygenase in Glioblastoma.

Abnormal circulation in solid tumors results in hypoxia, which modulates both tumor intrinsic malignant properties as well as anti-tumor immune responses. Given the importance of hypoxia in glioblastoma (GBM) biology and particularly in shaping anti-tumor immunity, we analyzed which immunomodulatory genes are differentially regulated in response to hypoxia in GBM cells. Gene expression analyses identified the immunosuppressive enzyme tryptophan-2,3-dioxygenase (TDO2) as the second most downregulated gene in GBM cells cultured under hypoxic conditions. TDO2 catalyses the oxidation of tryptophan to N-formyl kynurenine, which is the first and rate-limiting step of Trp degradation along the kynurenine pathway (KP). In multiple GBM cell lines hypoxia reduced TDO2 expression both at mRNA and protein levels. The downregulation of TDO2 through hypoxia was reversible as re-oxygenation rescued TDO2 expression. Computational modeling of tryptophan metabolism predicted reduced flux through the KP and lower intracellular concentrations of kynurenine and its downstream metabolite 3-hydroxyanthranilic acid under hypoxia. Metabolic measurements confirmed the predicted changes, thus demonstrating the ability of the mathematical model to infer intracellular tryptophan metabolite concentrations. Moreover, we identified hypoxia inducible factor 1α (HIF1α) to regulate TDO2 expression under hypoxic conditions, as the HIF1α-stabilizing agents dimethyloxalylglycine (DMOG) and cobalt chloride reduced TDO2 expression. Knockdown of HIF1α restored the expression of TDO2 upon cobalt chloride treatment, confirming that HIF1α controls TDO2 expression. To investigate the immunoregulatory effects of this novel mechanism of TDO2 regulation, we co-cultured isolated T cells with TDO2-expressing GBM cells under normoxic and hypoxic conditions. Under normoxia TDO2-expressing GBM cells suppressed T cell proliferation, while hypoxia restored the proliferation of the T cells, likely due to the reduction in kynurenine levels produced by the GBM cells. Taken together, our data suggest that the regulation of TDO2 expression by HIF1α may be involved in modulating anti-tumor immunity in GBM.

The Influence of Effect of Polysaccharides and Polyvinylpyrrolidone on the Photocatalytic Activity of Chlorin e6 in Tryptophan Oxidation

The effect amphiphic polymer poly-N-vinylpyrrolidone (PVP) and polysaccharides (PSs), sodium alginate (SA) and hyaluronic acid (HA), have on the photosensitizing activity of chlorin e6 (Ce6) in the reaction of tryptophan oxidation is established. This reaction is considered a model in searching for the most efficient pharmaceutical formulations of photosensitizers for antimicrobial photodynamic therapy. It is shown that the initial photosensitizing activity of Ce6, characterized by effective rate constant keff of tryptophan oxidation, grows as binary (Ce6–PVP and Ce6–SA(HA)) and (to a greater extent) ternary systems (Ce6–PVP–SA and Ce6–PVP–SA(HA)) form in aqueous solutions. This rise in activity is found to be related to disaggregation of the associates of photosensitizer (PhS) molecules initially present in aqueous solutions, resulting from the formation of complex bonds between PhS molecules and fragments of polymers added to the solution. This conclusion is confirmed for the considered binary and ternary systems by the accumulated data of electronic absorption spectra and fluorescence spectra of chlorin e6 in the absence of polymers (PVP, SA, and HA) and after they are added to the reaction system, and by 1H NMR data. In light of the most recent findings (according to which each polymeric component (PVP, SA, and HA) affects the activity of PhS, while almost no direct interaction between PVP and PS is detected in the 1H NMR spectra), ternary photosensitizing systems form in aqueous media during the formation of intertwining PVP–PS polymeric chains upon exposure to local hydrodynamic flows, followed by complex bonding between PhS molecules and fragments of both polymers.

Protective role of hesperetin against posttranslational oxidation of tryptophan residue of human γD-crystallin: A molecular level study

Crystallin proteins undergo various posttranslational modifications with aging of eye lens. Oxidation of tryptophan (Trp) residues of a major γ-crystallin namely human γD-crystallin (HGD) was found to be inhibited by a naturally occurring flavonoid hesperetin at relatively low concentration mostly due to its antioxidant activity. Further the molecular interactions between HGD and hesperetin were elucidated on the basis of the quenching of Trp fluorescence of the protein by the flavonoid. Ground state complexation between HGD and hesperetin caused static quenching of the Trp fluorescence of HGD. Binding and quenching constants were in the order of (103- 104 M−1). Energy transfer from protein to hesperetin was suggested by FRET calculations. Thermodynamic parameters reveal significant hydrophobic association between the protein and hesperetin. Synchronous fluorescence and CD spectroscopic results had ruled out conformational changes in the protein due to binding of hesperetin. Docking studies suggested the proximity of hesperetin with Trp 42, which largely corroborates our experimental findings.

Simultaneous voltammetric analysis of tryptophan and kynurenine in culture medium from human cancer cells

The paper outlines the first report of application of a differential pulse voltammetry for simultaneous quantification of clinically important molecular markers – tryptophan and its metabolite – kynurenine. The analytes were determined in less than 60 s at the boron-doped diamond electrode modified in situ with bismuth film (BiF/BDDE). Proper adjustment of a supporting electrolyte composition allowed to obtain good separation of tryptophan and kynurenine oxidation peaks that appeared at potential of 0.88 and 1.05 V (vs. Ag/AgCl), respectively. Studies using an optical profilometer have confirmed an increase in electrode surface area after deposition of Bi film. At the optimized conditions, the obtained detection limits of tryptophan and kynurenine were at 30 nM concentrations. The method was validated for linearity, precision, accuracy, selectivity and recovery. We have investigated an impact of numerous relevant interfering organic compounds (including amino acids and different tryptophan metabolites of kynurenine pathway) on voltammetric signals of the measured analytes. Finally, for proof˗of˗technology, the sensor was used for tryptophan and kynurenine quantification in culture medium collected from human cancer cell lines (breast MDA–MB–231 and ovary SK–OV–3). The target molecules were analyzed directly, without any sample preparation step. The sensor showed good accuracy in presence of the sample matrix components that was confirmed by high performance liquid chromatography measurements. Our work emphasizes the advantages of application of the herein proposed, easy to fabricate voltammetric sensor, instead of popular chromatographic assays or previously proposed potentiometric immunosensor. The method might serve for rapid assessment of kynurenine pathway activity in cancer cells.

Protection by ethyl pyruvate against gamma radiation induced damage in bovine serum albumin

Environmental factors like ionizing radiation induced generation of reactive oxygen species (ROS) cause macromolecular damage under physiological conditions. Proteins are the potential targets of ROS induced oxidative damage because of their abundance and their critical functions in the biological systems. The present study investigates the protective potential of ethyl pyruvate (EP) against ionizing radiation induced oxidative damage of bovine serum albumin (BSA) using spectroscopic, biochemical and SDS-PAGE techniques. Spectroscopic data shows that EP prevents the build up of protein damage markers like bityrosine formation and oxidation of tryptophan. Protein melting studies shows that the melting temperature (Tm) of the irradiated protein does not change significantly in the presence of EP. Biochemical assays indicate that ionizing radiation causes the generation of carbonyls and malondialdehyde and the loss of thiol content in proteins that is prevented by EP. The SDS-PAGE profile of gamma irradiated BSA shows the radioprotective effect of EP. These results indicate the radiation induced oxidative and molecular changes in the protein and that the EP protected the BSA from these modifications. Therefore, these results imply that EP has a good antiradical property and hence it can be proposed as a good radioprotective agent.

Dinitrosyl Iron Complexes in the Sensitized Oxidation of Organic Substrates

It is shown that the efficacy of the photosensitized oxidation of organic substrates in aqueous media (with the oxidation of tryptophan being used as an example) does not depend on adding biologically active dinitrosyl iron complexes (DNICs) with thiol-containing ligands to the reaction medium if it contains Pluronic F127, a poly(ethylene oxide)–poly(propylene oxide)– poly(ethylene oxide) triblock copolymer, at concentrations higher than the critical micelle concentration. Photosensitizer molecules are localized in Pluronic micelles and are shielded from the damaging impact of NO• radicals that form upon the photodegradation of DNIC molecules. Photodynamic therapy (PDT) sessions (the photoinduced necrosis and apoptosis of cells in pathologically altered tissues and the simultaneous initiation of regeneration and repair of the treated tissues due to the photodecomposition of DNIC molecules) thus become fundamentally possible.

Peroxymonosulfate Oxidizes Amino Acids in Water without Activation.

A variety of peptidic and proteinaceous contaminants (e.g., proteins, toxins, pathogens) present in the environment may pose risk to human health and wildlife. Peroxymonosulfate is a strong oxidant (EH0 = 1.82 V for HSO5-, the predominant species at environmental pH values) that may hold promise for the deactivation of proteinaceous contaminants. Relatively little quantitative information exists on the rates of peroxymonosulfate reactions with free amino acids. Here, we studied the oxidation of 19 of the 20 standard proteinogenic amino acids (all except cysteine) by peroxymonosulfate without explicit activation. Reaction half-lives at pH 7 ranged from milliseconds to hours. Amino acids possessing sulfur-containing, heteroaromatic, or substituted aromatic side chains were the most susceptible to oxidation by peroxymonosulfate, with rates of transformation decreasing in the order methionine > tryptophan > tyrosine > histidine. The rate of tryptophan oxidation did not decrease in the presence of an aquatic natural organic matter. Singlet oxygen resulting from peroxymonosulfate self-decomposition, while detected by electron paramagnetic resonance spectroscopy, was unlikely to be the principal reactive species. Our results demonstrate that peroxymonosulfate is capable of oxidizing 19 amino acids without explicit activation and that solvent-exposed methionine and tryptophan residues are likely initial targets of oxidation in peptides and proteins.

Poly(3,4-ethylenedioxythiophene)-modified electrodes for tryptophan voltammetric sensing

Poly(3,4-ethylenedioxythiophene) (PEDOT) layers are obtained by electrochemical polymerization under potentiostatic (PS) or sinusoidal voltage (SV) control using aqueous solutions containing either polystyrene sulfonate (PSS) or dodecyl sulfate (SDS) doping ions. The parameters of the SV procedure are adjusted in a way to have PEDOT layers with capacitive charging/discharging currents similar to the ones of PS-deposited PEDOTs. Tryptophan (TRP) oxidation is studied by voltammetry in solutions with pH ranging from 4 to 9 and pH7 is chosen for electroanalytical studies. All four types of PEDOT layers show linear concentration dependence of the voltammetric peak currents in extended concentration range (10–400μM). It is found that the electroanalytical parameters (sensitivity, LOD and range of linear response) do not depend on the nature of the dopant and the electrochemical method used to obtain the PEDOT coatings. No fouling of the PEDOT-coated electrodes is observed after intensive exposure to TRP. Interference studies demonstrate the feasibility of PEDOT as sensing material in the presence of dopamine, uric and ascorbic acids. Recovery studies performed in urine and human serum samples demonstrate good anti-matrix capability of the developed sensing layers.