Standards-Free Absolute Quantitation of Oxidizable Glycopeptides by Coulometric Mass Spectrometry

Currently, glycopeptide quantitation is mainly based on relative quantitation due to absolute quantitation requiring isotope-labeled or standard glycopeptides which may not be commercially available or are very costly and time consuming to synthesize. To address this grand challenge, coulometric mass spectrometry (CMS), based on the combination of electrochemistry (EC) and mass spectrometry (MS), was utilized to quantify electrochemically active glycopeptides without the need of using standard materials. In this study, we studied tyrosine-containing glycopeptides, NYIVGQPSS(β-GlcNAc)TGNL-OH and NYSVPSS(β-GlcNAc)TGNL-OH, and successfully quantified them directly with CMS with a discrepancy of less than 5% between the CMS measured amount and the theoretical amount. Taking one step further, we applied this approach to quantify glycopeptides generated from the digestion of NIST mAb, a monoclonal antibody reference material. Through HILIC column separation, five N297 glycopeptides resulting from NIST mAb tryptic digestion were successfully separated and quantified by CMS for an absolute amount without the use of any standard materials. This study indicates the potential utility of CMS for quantitative proteomics research.

Electrochemical Synthesis of Molecularly Imprinted Polymers for L-Tyrosine Detection

L-Tyrosine (L-Tyr), a critical amino acid whose aberrant levels impact melanin and dopamine levels in human body while also increasing insulin resistance thereby increasing the risk of type 2 diabetes. The objective of this study was to detect the amount of L-Tyr in human fluids by tailored electrochemical synthesis of well adhered, homogenous and thin molecularly imprinted polymers (MIPs) by the electro-polymerization of pyrrole on glassy carbon electrode modified functionalized multi-walled carbon nanotubes. The key benefits of this procedure over previous imprinting techniques were the elimination of expensive materials like Au and tedious multi-step synthesis, for L-Tyr detection using a handheld potentiostat. The developed particles were characterized using Fourier Transform Infrared Spectroscopy, Scanning Electron Microscope, Chronoamperometry, and Cyclic Voltammetry. With strong reproducibility and stability, this optimized approach provides a rapid and effective method of preparing and sensing MIPs for the target analyte with a broad linear range of [Formula: see text] to [Formula: see text]. The Limit of Detection and Limit of Quantification were [Formula: see text] and [Formula: see text], respectively. The engineered sensor was validated for quantifying the concentrations of L-Tyr in human blood and serum samples, yielding satisfactory recovery and can be expanded in future to detect analytes simultaneous.

Tripeptide-Assisted Gold Nanocluster Formation for Fe3+ and Cu2+ Sensing

Fluorescent gold nanoclusters (AuNCs) have shown promise as metal ion sensors. Further research into surface ligands is crucial for developing sensors that are both selective and sensitive. Here, we designed simple tripeptides to form fluorescent AuNCs, capitalizing on tyrosine's reduction capability under alkaline conditions. We investigated tyrosine's role in both forming AuNCs and sensing metal ions. Two tripeptides, tyrosine-cysteine-tyrosine (YCY) and serine-cysteine-tyrosine (SCY), were used to form AuNCs. YCY peptides produced AuNCs with blue and red fluorescence, while SCY peptides produced blue-emitting AuNCs. The blue fluorescence of YCY- and SCY-AuNCs was selectively quenched by Fe3+ and Cu2+, whereas red-emitting YCY-AuNC fluorescence remained stable with 13 different metal ions. The number of tyrosine residues influenced the sensor response. DLS measurements revealed different aggregation propensities in the presence of various metal ions, indicating that chelation between the peptide and target ions led to aggregation and fluorescence quenching. Highlighting the innovation of our approach, our study demonstrates the feasibility of the rational design of peptides for the formation of fluorescent AuNCs that serve as highly selective and sensitive surface ligands for metal ion sensing. This method marks an advancement over existing methods due to its dual capability in both synthesizing gold nanoclusters and detecting analytes, specifically Fe3+ and Cu2+.

Germination Increases the Glucomoringin Content in Moringa Sprouts via Transforming Tyrosine

Moringa seeds are an excellent dietary source of phytochemicals (i.e., glucosinolates, GSLs; isothiocyanates, ITCs) with health-beneficial effects. Although numerous studies have been conducted on moringa seeds, the effect of germination on the regulation of GSLs remains scarcely explored. The present study investigated the dynamic changes of GSLs in moringa seeds during germination (at 25, 30, and 35 °C for 6 days in the dark) through an untargeted metabolomics approach and compared the antioxidant capacity of ungerminated and germinated moringa seeds. Our results showed that germination significantly increased the total GSL content from 150 (day 0) to 323 μmol/g (35 °C, day 6) on a dry weight (DW) basis, especially glucomoringin (GMG), the unique glucosinolate in moringa seeds, which was significantly upregulated from 61 (day 0) to 149 μmol/g DW (35 °C, day 4). The upregulation of GMG corresponded to the metabolism of tyrosine, which might be the initial precursor for the formation of GMG. In addition, germination enhanced the total ITC content from 85 (day 0) to 239 μmol SE/g DW (35 °C, day 6), indicating that germination may have also increased the activity of myrosinase. Furthermore, germination remarkably increased the total phenolic content (109-507 mg GAE/100 g DW) and antioxidant capacity of moringa seeds. Our findings suggest that moringa sprouts could be promoted as a novel food and/or ingredient rich in GMG.

Impact of phenylalanine on Hanseniaspora vineae aroma metabolism during wine fermentation

Hanseniaspora vineae exhibits extraordinary positive oenological characteristics contributing to the aroma and texture of wines, especially by its ability to produce great concentrations of benzenoid and phenylpropanoid compounds compared with conventional Saccharomyces yeasts. Consequently, in practice, sequential inoculation of H. vineae and Saccharomyces cerevisiae allows to improve the aromatic quality of wines. In this work, we evaluated the impact on wine aroma produced by increasing the concentration of phenylalanine, the main amino acid precursor of phenylpropanoids and benzenoids. Fermentations were carried out using a Chardonnay grape juice containing 150 mg N/L yeast assimilable nitrogen. Fermentations were performed adding 60 mg/L of phenylalanine without any supplementary addition to the juice. Musts were inoculated sequentially using three different H. vineae strains isolated from Uruguayan vineyards and, after 96 h, S. cerevisiae was inoculated to complete the process. At the end of the fermentation, wine aromas were analysed by both gas chromatography-mass spectrometry and sensory evaluation through a panel of experts. Aromas derived from aromatic amino acids were differentially produced depending on the treatments. Sensory analysis revealed more floral character and greater aromatic complexity when compared with control fermentations without phenylalanine added. Moreover, fermentations performed in synthetic must with pure H. vineae revealed that even tyrosine can be used in absence of phenylalanine, and phenylalanine is not used by this yeast for the synthesis of tyrosine derivatives.

Impact of dietary supplementation with N-carbamoyl-aspartic acid on serum metabolites and intestinal microflora of sows

BACKGROUND

N-Carbamoyl-aspartic acid (NCA) is a critical precursor for de novo biosynthesis of pyrimidine nucleotides. To investigate the cumulative effects of maternal supplementation with NCA on the productive performance, serum metabolites and intestinal microbiota of sows, 40 pregnant sows (∼day 80) were assigned into two groups: (1) the control (CON) and (2) treatment (NCA, 50 g t^-1 NCA).

RESULTS

Results showed that piglets from the NCA group had heavier birth weight than those in the CON group (P < 0.05). In addition, maternal supplementation with NCA decreased the backfat loss of sows during lactation (P < 0.05). Furthermore,16S-rRNA sequencing results revealed that maternal NCA supplementation decreased the abundance of Cellulosilyticum, Fournierella, Anaerovibrio, and Oribacterium genera of sows during late pregnancy (P < 0.05). Similarly, on the 14th day of lactation, maternal supplementation with NCA reduced the diversity of fecal microbes of sows as evidenced by significantly lower observed species, Chao1, and Ace indexes, and decreased the abundance of Lachnospire, Faecalibacterium, and Anaerovorax genera, while enriched the abundance of Catenisphaera (P < 0.05). Untargeted metabolomics showed that a total of 48 differentially abundant biomarkers were identified, which were mainly involved in metabolic pathways of arginine/proline metabolism, phenylalanine/tyrosine metabolism, and fatty acid biosynthesis, etc. CONCLUSION: Overall, the results indicated that NCA supplementation regulated intestinal microbial composition of sows and serum differential metabolites related to arginine, proline, phenylalanine, tyrosine, and fatty acids metabolism that may contribute to regulating the backfat loss of sows, and the birth weight and diarrhea rate of piglets. © 2022 Society of Chemical Industry.

Associations of forest negative air ions exposure with cardiac autonomic nervous function and the related metabolic linkages: A repeated-measure panel study

Forest environment has many health benefits, and negative air ions (NAI) is one of the major forest environmental factors. Many studies have explored the effect of forest environment on cardiac autonomic nervous function, while forest NAI in the among function and the underlying mechanism still remain unclear. To explore the associations and molecular linkages between short-term exposure to forest NAI and heart rate variability (HRV), a repeated-measure panel study was conducted among 31 healthy adults. Participants were randomly selected to stay in a forest park for 3 days and 2 nights. Individual exposures including NAI were monitored simultaneously and HRV indices were measured repeatedly at the follow-up period. Urine samples were collected for non-targeted metabolomics analysis. Mixed-effect models were adopted to evaluate associations among NAI, HRV indices and metabolites. The median of NAI concentration was 68.11 (138.20) cm^-3 during the study period. Short-term exposure to forest NAI was associated with the ameliorative HRV indices, especially the excitatory parasympathetic nerve. For instance, per interquartile range increase of 5-min moving average of NAI was associated with 9.99 % (95%CI: 8.95 %, 11.03 %) increase of power in high frequency. Eight metabolites were associated with NAI exposure. The down-regulated tyrosine metabolism was firstly observed, followed by other amino acid metabolic alterations. The NAI-related metabolic changes reflect the reduction of inflammation and oxidative stress. HRV indices were associated with 25 metabolites, mainly including arginine, proline and histidine metabolism. Short-term exposure to forest NAI is beneficial to HRV, especially to the parasympathetic nerve activity, by successively disturbing different metabolic pathways which mainly reflect the increased anti-inflammation and the reduced inflammation. The results will provide epidemiological evidences for developing forest therapy and improving cardiac autonomic nervous function.

A Review of Sensors and Biosensors Modified with Conducting Polymers and Molecularly Imprinted Polymers Used in Electrochemical Detection of Amino Acids: Phenylalanine, Tyrosine, and Tryptophan

Recently, the studies on developing sensors and biosensors-with an obvious interdisciplinary character-have drawn the attention of many researchers specializing in various fundamental, but also complex domains such as chemistry, biochemistry, physics, biophysics, biology, bio-pharma-medicine, and bioengineering. Along these lines, the present paper is structured into three parts, and is aimed at synthesizing the most relevant studies on the construction and functioning of versatile devices, of electrochemical sensors and biosensors, respectively. The first part presents examples of the most representative scientific research focusing on the role and the importance of the phenylalanine, tyrosine, and tryptophan amino acids, selected depending on their chemical structure and their impact on the central nervous system. The second part is dedicated to presenting and exemplifying conductor polymers and molecularly imprinted polymers used as sensitive materials in achieving electrochemical sensors and biosensors. The last part of the review analyzes the sensors and biosensors developed so far to detect amino acids with the aid of conductor polymers and molecularly imprinted polymers from the point of view of the performances obtained, with emphasis on the detection methods, on the electrochemical reactions that take place upon detection, and on the electroanalytical performances. The present study was carried out with a view to highlighting, for the benefit of specialists in medicine and pharmacy, the possibility of achieving and purchasing efficient devices that might be used in the quality control of medicines, as well as in studying and monitoring diseases associated with these amino acids.

Spectrophotometric Assays for Sensing Tyrosinase Activity and Their Applications

Tyrosinase (TYR, E.C. 1.14.18.1), a critical enzyme participating in melanogenesis, catalyzes the first two steps in melanin biosynthesis including the ortho-hydroxylation of L-tyrosine and the oxidation of L-DOPA. Previous pharmacological investigations have revealed that an abnormal level of TYR is tightly associated with various dermatoses, including albinism, age spots, and malignant melanoma. TYR inhibitors can partially block the formation of pigment, which are always used for improving skin tone and treating dermatoses. The practical and reliable assays for monitoring TYR activity levels are very useful for both disease diagnosis and drug discovery. This review comprehensively summarizes structural and enzymatic characteristics, catalytic mechanism and substrate preference of TYR, as well as the recent advances in biochemical assays for sensing TYR activity and their biomedical applications. The design strategies of various TYR substrates, alongside with several lists of all reported biochemical assays for sensing TYR including analytical conditions and kinetic parameters, are presented for the first time. Additionally, the biomedical applications and future perspectives of these optical assays are also highlighted. The information and knowledge presented in this review offer a group of practical and reliable assays and imaging tools for sensing TYR activities in complex biological systems, which strongly facilitates high-throughput screening TYR inhibitors and further investigations on the relevance of TYR to human diseases.

Development of Polypyrrole Modified Screen-Printed Carbon Electrode Based Sensors for Determination of L-Tyrosine in Pharmaceutical Products

Good health, of vital importance in order to carry out our daily routine, consists of both physical and mental health. Tyrosine (Tyr) deficiency as well as its excess are issues that can affect mental health and can generate disorders such as depression, anxiety, or stress. Tyr is the amino acid (AA) responsible for maintaining good mental health, and for this reason, the present research presents the development of new electrochemical sensors modified with polypyrrole (PPy) doped with different doping agents such as potassium hexacyanoferrate (II) (FeCN), sodium nitroprusside (NP), and sodium dodecyl sulfate (SDS) for a selective and sensitive detection of Tyr. The development of the sensors was carried out by chronoamperometry (CA) and the electrochemical characterization was carried out by cyclic voltammetry (CV). The detection limits (LOD) obtained with each modified sensor were 8.2 × 10-8 M in the case of PPy /FeCN-SPCE, 4.3 × 10-7 M in the case of PPy/NP-SPCE, and of 3.51 × 10-7 M in the case of PPy/SDS-SPCE, thus demonstrating a good sensitivity of these sensors detecting L-Tyr. The validation of sensors was carried out through quantification of L-Tyr from three pharmaceutical products by the standard addition method with recoveries in the range 99.92-103.97%. Thus, the sensors present adequate selectivity and can be used in the pharmaceutical and medical fields.

Pyrene-Based AIEE Active Nanoprobe for Zn2+ and Tyrosine Detection Demonstrated by DFT, Bioimaging, and Organic Thin-Film Transistor

The development of aggregation-induced emission enhancement (AIEE) active nanoprobes without any synthetic complication for solution-state and organic thin-film transistor (OTFT)-based sensory applications is still a challenging task. In this study, the novel pyrene-incorporated Schiff base (5-phenyl-4-((pyren-1-ylmethylene)amino)-4H-1,2,4-triazole-3-thiol; PT2) with an AIEE property was synthesized via a one-pot reaction and was reported for detecting Zn²⁺ and tyrosine in the solution state and OTFT. In the AIEE studies of PT2 (in CH₃CN) at various water fractions (f_w: 0-97.5%), the existence of J-aggregation, crystalline changes, and nanofibers formation was confirmed by ultraviolet absorption/photoluminescence (UV/PL) spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic-light scattering (DLS) techniques. Similarly, PT2-based Zn²⁺ detection and sensory reversibility with tyrosine were demonstrated by UV/PL studies with evidence related to crystalline/nanolevel changes in PXRD, SEM, TEM, AFM, and DLS data. Distinct decay profiles associated with the AIEE and sensory responses of PT2 were observed in time-resolved photoluminescence spectra. From the standard deviation and linear fittings of PL titrations, detection limits (LODs) of the Zn²⁺ with PT2 and the tyrosine with PT2-Zn²⁺ were estimated as 0.79 and 45 nM, respectively. High-resolution mass and ¹H NMR results confirmed 2:1 and 1:1 stoichiometry and binding sites of PT2-Zn²⁺-PT2* and tyrosine-Zn²⁺ complexes. Moreover, the values of association constants determined by linear fittings were 4.205 × 10^-7 and 1.73 × 10^-8 M^-2, correspondingly. Optimization via the density functional theory disclosed the binding sites and suppression of twisted intramolecular charge transfer/photoinduced electron transfer (TICT/PET) as well as the involvement of restricted intramolecular rotation in the AIEE and PET "ON-OFF-ON" mechanisms in the Zn²⁺ and tyrosine sensors. Results from the B16-F10 cellular and zebrafish imaging of AIEE, Zn²⁺, and tyrosine sensors further attested the applicability of PT2 in biological samples. Finally, the PT2 and pentacene-incorporated OTFT devices were fabricated. The devices displayed more than 90% change in drain-source current when reacted with Zn²⁺ with an LOD of 5.46 μM but showed no response to tyrosine, thereby confirming the reversibility. Moreover, the OTFT devices also demonstrated Zn²⁺ ion detection in tap water and lake water samples.

Site-specific identification and validation of hepatic histone nitration in vivo: Implications for alcohol-induced liver injury

Oxidative and nitrative stress have been implicated in the molecular mechanisms underlying a variety of biological processes and disease states including cancer, aging, cardiovascular disease, neurological disorders, diabetes, and alcohol-induced liver injury. One marker of nitrative stress is the formation of 3-nitrotyrosine, or protein tyrosine nitration (PTN), which has been observed during inflammation and tissue injury; however, the role of PTN in the progression or possibly the pathogenesis of disease is still unclear. We show in a model of alcohol-induced liver injury that an increase in PTN occurs in hepatocyte nuclei within the liver of wild-type male C57BL/6J mice following chronic ethanol exposure (28 days). High-resolution mass spectrometric analysis of isolated hepatic nuclei revealed several novel sites of tyrosine nitration on histone proteins. Histone nitration sites were validated by tandem mass spectrometry (MS/MS) analysis of representative synthetic nitropeptides equivalent in sequence to the respective nitrotyrosine sites identified in vivo. We further investigated the potential structural impact of the novel histone H3 Tyr41 (H3Y41) nitration site identified using molecular dynamics (MD) simulations. MD simulations of the nitrated and non-nitrated forms of histone H3Y41 showed significant structural changes at the DNA interface upon H3Y41 nitration. The results from this study suggest that, in addition to other known post-translational modifications that occur on histone proteins (e.g., acetylation and methylation), PTN could induce chromatin structural changes, possibly affecting gene transcription processes associated with the development of alcohol-induced liver injury.

A Method for Analysis of Nitrotyrosine-Containing Proteins by Immunoblotting Coupled with Mass Spectrometry

Nitrotyrosine formation is caused by presence of reactive oxygen and nitrogen species. Nitration is a very selective process leading to specific modification of only a few tyrosines in protein molecule. 2D electrophoresis and western blotting techniques coupled with mass spectrometry are common methods used in analysis of proteome. Here we describe protocol for analysis of peroxynitrite-induced protein nitration in isolated mitochondria. Mitochondrial proteins are separated by 2D electrophoresis and transferred to nitrocellulose membrane. Membranes are then incubated with antibodies against nitrotyrosine. Positive spots are compared with corresponding Coomassie-stained gels, and protein nitration is confirmed with mass spectrometry techniques.

Composition, source, and influencing factors of white spots formation in soybean paste

White spots are commonly found in bean-based fermented food, which will significantly lower the product quality. This study aimed to analyze the composition of white spots and further reveal the source and influencing factors of white spots in bean-based fermented food using soybean paste as study model. The results showed that white spots were mainly composed of 40.96% free tyrosine and 37.94% tyrosine in combination form. During soybean paste fermentation, tyrosine was found to be produced by the actions of proteolytic enzymes secreted by Aspergillus oryzae 3.042 instead of the microbial metabolism and the excessive accumulation of tyrosine in soybean paste led to the formation of white spots. Among all influencing factors, high temperature treatment favored the formation of white spots. The existence of soy peptone and phenylalanine would postpone the precipitation of tyrosine while promoting the aggregation of the tyrosine precipitation. Field emission scanning electron microscope analysis showed that tyrosine would accumulate around the soybean protein particles and treatment at 120 °C would disrupt the structure of tyrosine-protein complex. Based on the above results, we proposed that treatment of soybean paste at temperature lower than 80 °C was the current practically applicable method to control the formation of white spots in soybean paste. PRACTICAL APPLICATION: This study developed a new idea to understand the composition and formation of white spots in soybean paste, which would provide guidance for prevention and control of white spots during the production of soybean paste for manufacturers and researchers.

Development of molecular and histological methods to evaluate stress oxidative biomarkers in sea bass (Dicentrarchus labrax)

In aquaculture, fish species may experience stressful episodes caused by poor farming conditions. The exponential increase of global aquaculture has raised the number of research studies aimed at demonstrating the sensitivity of aquatic animals in confined environments. The development of a real-time PCR and immunohistochemistry methods were investigated to evaluate the presence, localization, and quantity of biomarkers of oxidative stress in European sea bass (Dicentrarchus labrax). In particular, stress tests such as manipulation and temperature changes were conducted through molecular methods to identify the expression level of heat shock protein 70 (HSP70) in stressed animals compared with a control group. The immunohistochemical technique was also applied to locate and study the trends-levels of nitrotyrosine (NT), heat shock protein 70 (HSP70), malondialdehyde (MDA), and 4-hydroxy-2-nonenal (HNE) in different tissues from stressed animals and control group. The presence of the rodlet cell (RCs) was evaluated by histology in both a control and stressed group. Our results show that the real-time PCR method developed is specific for the evaluated target gene and that manipulation and temperature increase are strong stressors for animals. Relative quantification data revealed a gene expression increase of HSP70 in the stressed group of animals compared to the control group. The antibodies used for the immunohistochemical staining were efficient, and it was possible to appreciate the increase of immunoprecipitates in European sea bass either manipulated or stressed by temperature increase. The present study can be a starting point to allow the quantification of HSP70 and the identification of other stress biomarkers in D. labrax.

Colorimetric dual sensor for Cu(II) and tyrosine and its application as paper strips for detection in water and human saliva as real samples

A calix[4]arene based compound incorporating amide and morpholine moieties has been synthesized and its ion recognition property towards metal ions and application of its metal complex towards sensing of amino acids has been investigated. The synthesized compound interacts with Cu²⁺ with high selectivity and sensitivity (LOD, 0.1 ppb) in aqueous media with instant color change from colorless to yellow without interference from any other metal ions used in this study. The molecular structure of the calix compound (1) has been determined by single crystal X-ray study and the structure of its Cu²⁺ complex has been established by DFT calculation. The Cu²⁺ complex of 1 selectively detects tyrosine (LOD, 1.2 ppm) in water with distinct color change and without any interference from other 22 amino acids used in this study. The mechanism for detection of tyrosine with color change is also presented. For easy field application, paper based sensor strips have been prepared by coating compound 1 and its Cu²⁺ complex on filter paper, which have been used for semi-quantitative measurement of Cu²⁺ and tyrosine. Compound 1 and its Cu²⁺ complex have also been used for detection of Cu²⁺ and tyrosine, respectively in water and human saliva as real samples and satisfactory results are obtained.

Signature Fragment Ions of Biotinylated Peptides

The use of biotin or biotin-containing reagents is an essential component of many protein purification and labeling technologies. Owing to its small size and high affinity to the avidin family of proteins, biotin is a versatile molecular handle that permits both enrichment and purity that is not easily achieved by other reagents. Traditionally, the use of biotinylation to enrich for proteins has not required the detection of the site of biotinylation. However, newer technologies for discovery of protein-protein interactions, such as APEX and BioID, as well as some of the click chemistry-based labeling approaches have underscored the importance of determining the exact residue that is modified by biotin. Anti-biotin antibody-based enrichment of biotinylated peptides (e.g., BioSITe) coupled to LC-MS/MS permit large-scale detection and localization of sites of biotinylation. As with any chemical modification of peptides, understanding the fragmentation patterns that result from biotin modification is essential to improving its detection by LC-MS/MS. Tandem mass spectra of biotinylated peptides has not yet been studied systematically. Here, we describe the various signature fragment ions generated with collision-induced dissociation of biotinylated peptides. We focused on biotin adducts attached to peptides generated by BioID and APEX experiments, including biotin, isotopically heavy biotin, and biotin-XX-phenol, a nonpermeable variant of biotin-phenol. We also highlight how the detection of biotinylated peptides in high-throughput studies poses certain computational challenges for accurate quantitation which need to be addressed. Our findings about signature fragment ions of biotinylated peptides should be helpful in the confirmation of biotinylation sites.

Adhesive Properties of Adsorbed Layers of Two Recombinant Mussel Foot Proteins with Different Levels of DOPA and Tyrosine

Using a surface forces apparatus and an atomic force microscope, we characterized the adhesive properties of adsorbed layers of two recombinant variants of Perna viridis foot protein 5 (PVFP-5), the main surface-binding protein in the adhesive plaque of the Asian green mussel. In one variant, all tyrosine residues were modified into 3,4-dihydroxy-l-phenylalanine (DOPA) during expression using a residue-specific incorporation strategy. DOPA is a key molecular moiety underlying underwater mussel adhesion. In the other variant, all tyrosine residues were preserved. The layer was adsorbed on a mica substrate and pressed against an uncoated surface. While DOPA produced a stronger adhesion than tyrosine in contact with the nanoscopic Si₃N₄ probe of the atomic force microscope, the two variants produced comparable adhesion on the curved macroscopic mica surfaces of the surface forces apparatus. These findings show that the presence of DOPA is not a sufficient condition to generate strong underwater adhesion. Surface chemistry and contact geometry affect the strength and abundance of protein-surface bonds created during adsorption and surface contact. Importantly, the adsorbed protein layer has a random and dynamic polymer-network structure that should be optimized to transmit the tensile stress generated during surface separation to DOPA surface bonds rather than other weaker bonds.

Biometals as conformational modulators of α-synuclein photochemical crosslinking

Metal dyshomeostasis has long been linked to Parkinson's disease (PD), and the amyloidogenic protein α-synuclein (αS) is universally recognized as a key player in PD pathology. Structural consequences upon coordination of copper and iron to αS have gained attention due to significant dyshomeostasis of both metals in the PD brain. Protein-metal association can navigate protein folding in distinctive pathways based on the identity of the bio-metal in question. In this work, we employed photo-chemical crosslinking of unmodified proteins (PICUP) to evaluate these potential metal ion-induced structural alterations in the folding dynamics of N-terminally acetylated αS (NAcαS) following metal coordination. Through fluorescence analysis and immunoblotting analyses following photoirradiation, we discovered that coordination of iron obstructs copper-promoted crosslinking. The absence of intra-molecular crosslinking upon iron association further supports its C-terminal coordination site and suggests a potential role for iron in mitigating nearby post-translational modification of tyrosine residues. Decreased fluorescence emission upon synergistic coordination of both copper and iron highlighted that although copper acts as a conformational promotor of NAcαS crosslinking, iron inhibits analogous conformational changes within the protein. The metal coordination preferences of NAcαS suggest that both competitive binding sites as well as dual metal coordination contribute to the changes in folding dynamics, unveiling unique structural orientations for NAcαS that have a direct and measureable influence on photoinitiated dityrosine crosslinks. Moreover, our findings have physiological implications in that iron overload, as is associated with PD-insulted brain tissue, may serve as a conformational block of copper-promoted protein oxidation.

Absolute Quantitation of Oxidizable Peptides by Coulometric Mass Spectrometry

Quantitation methods for peptides using mass spectrometry have advanced rapidly. These methods rely on using standard and/or isotope-labeled peptides, which might be difficult or expensive to synthesize. To tackle this challenge, we present a new approach for absolute quantitation without the use of standards or calibration curves based on coulometry combined with mass spectrometry (MS). In this approach, which we call coulometric mass spectrometry (CMS), the mass spectrum of a target peptide containing one or more tyrosine residues is recorded before and after undergoing electrochemical oxidation. We record the total integrated oxidation current from the electrochemical measurement, which according to the Faraday's Law of coulometry, provides the number of moles of oxidized peptide. The ion intensity ratio of the target peptide before and after oxidation provides an excellent estimate of the fraction of the peptide that has been oxidized, from which the total amount of peptide is calculated. The striking strength of CMS is that it needs no standard peptide, but CMS does require the peptide to contain a known number of oxidizable groups. To illustrate the power of this method, we analyzed various tyrosine-containing peptides such as GGYR, DRVY, oxytocin, [Arg⁸]-vasotocin and angiotensinogen 1-14 with a quantification error ranging from - 7.5 to + 2.4%. This approach is also applicable to quantifying phosphopeptides and could be useful in proteomics research.

Characterization of the Site-Specific Acid-Base Equilibria of 3-Nitrotyrosine

The complete macro- and microequilibrium analyses of 3-nitrotyrosine, a biomarker of oxidative stress damage, are presented for the first time. The protonation macroconstants were determined by ¹ H-NMR-pH titration, while microconstants were elucidated by a combination of deductive and NMR methods, in which properties of the methyl ester derivative as an auxiliary compound were also studied. Combination of the NMR-pH characterization of the title and auxiliary compounds and the pair-interactivity parameters of 3-iodotyrosine provided the sufficient system to evaluate all the microconstants. NMR-pH profiles, macroscopic and microscopic protonation schemes, and species-specific distribution diagrams are included. The phenolate basicity of 3-nitrotyrosine is 500 times below that of tyrosine, and it is even lower than that of 3-iodotyrosine. This phenomenon can be explained by the stronger electron withdrawing and the negative mesomeric effect of the nitro group. Based on our results, 89 % of the phenolic OH groups are deprotonated in 3-NT molecules at the pH of the blood plasma.

Effect of low-temperature storage on the content of folate, vitamin B6 , ascorbic acid, chlorogenic acid, tyrosine, and phenylalanine in potatoes

BACKGROUND

Changes in the metabolite composition of potato tubers during low-temperature storage can affect their nutritional value, susceptibility to bruising, and processing qualities. Here, we measured changes in the amounts of folate, vitamin B₆ , and vitamin C, and the blackspot pigment precursors chlorogenic acid and tyrosine, as well as phenylalanine, in five potato varieties stored at 7.8 °C for 8 months in 2015 and 2016.

RESULTS

Folate content increased in all varieties in both years during low-temperature storage, with statistically significant changes occurring in six out of eight conditions. Increase rates ranged from 11% to 141%. Vitamin B₆ content increased in all varieties during the storage period, but changes were statistically significant in only two out of eight conditions. Increase rates ranged from 5% to 24%. Ascorbic acid content decreased in all varieties in both years during the storage period. Decrease rates ranged from 16% to 78%, and were statistically significant in seven out of eight conditions. For chlorogenic acid, no consistent trend was observed. Changes varied between -14% and +14%, but none was statistically significant. Tyrosine content increased in all varieties in both years, except in Sage Russet in 2015. Increase rates ranged from 19% to 238% and were statistically significant in three out of seven conditions. Changes in phenylalanine content were very similar to those observed for tyrosine, with increases up to 272% in Teton Russet.

CONCLUSIONS

These results show that storage at low temperature substantially affects tuber nutritional quality and biochemical bruising potential. © 2019 Society of Chemical Industry.

Efficiency of three intracellular extraction methods in the determination of metabolites related to tryptophan and tyrosine in winemaking yeast's metabolism by LC-HRMS

Yeast nitrogen metabolism produces metabolites, whose origin in wines has scarcely been studied, with an important biological and organoleptic role. The present work focuses on comparing three intracellular extraction methods in order to elucidate efficiency of extraction while measuring the effect of temperature upon the integrity of the compounds related to the metabolism of tryptophan and tyrosine by yeast. Two UHPLC/HRMS methods to measure 16 metabolites were developed and validated. The validation provided optimum values of LOD (7.4·10^-6 to 0.1 μg L^-1), of LOQ (2·10^-5 to 0.02 μg L^-1) of precision (11-0.5% RSD) and repeatability (12-0.5% RSD). The removal of interfering molecules enabled matrix effects to be kept at low levels. The results pointed out that the low-temperature methods were more effective, providing better precision for 16 metabolites. The high-temperature extraction method may yield false enhanced compounds concentrations since they originate in cell wall macromolecules degradation.

Express Method for Isolation of Ready-to-Use 3D Chitin Scaffolds from Aplysina archeri (Aplysineidae: Verongiida) Demosponge

Sponges are a valuable source of natural compounds and biomaterials for many biotechnological applications. Marine sponges belonging to the order Verongiida are known to contain both chitin and biologically active bromotyrosines. Aplysina archeri (Aplysineidae: Verongiida) is well known to contain bromotyrosines with relevant bioactivity against human and animal diseases. The aim of this study was to develop an express method for the production of naturally prefabricated 3D chitin and bromotyrosine-containing extracts simultaneously. This new method is based on microwave irradiation (MWI) together with stepwise treatment using 1% sodium hydroxide, 20% acetic acid, and 30% hydrogen peroxide. This approach, which takes up to 1 h, made it possible to isolate chitin from the tube-like skeleton of A. archeri and to demonstrate the presence of this biopolymer in this sponge for the first time. Additionally, this procedure does not deacetylate chitin to chitosan and enables the recovery of ready-to-use 3D chitin scaffolds without destruction of the unique tube-like fibrous interconnected structure of the isolated biomaterial. Furthermore, these mechanically stressed fibers still have the capacity for saturation with water, methylene blue dye, crude oil, and blood, which is necessary for the application of such renewable 3D chitinous centimeter-sized scaffolds in diverse technological and biomedical fields.

Effect of GO nanosheets on spectrophotometric determination of tyrosine in urine and serum using nitrosonaphthol

Here, we aimed to use graphene oxide to improve the selectivity and sensitivity of Tyr determination via the reaction with 1-nitroso-2-naphthol as a selective reagent of Tyr. The reaction between Tyr and 1-nitroso-2-naphthol in absence and presence of GO was studied spectrophotometrically. Different parameters such as concentrations, temperature, incubation time were optimized. The obtained data showed that the maximum absorbance was achieved by using 2 mL of 0.03% 1-nitroso-2-naphthol at temperature 60 °C for 10 min. On the basis of calibration curve of various concentrations of Tyr in the presence of 20 μg mL^-1 GO, the limit of detection was 6.4 × 10^-6 M (1.15 μg mL^-1), where in absence of GO was 1.1 × 10^-5 M (19.9 μg mL^-1). The selectivity of Tyr in presence of other amino acids and phenols was studied with and without GO. The data obtained revealed that the selectivity of Tyr in presence of GO with respect to some amino acids and phenols was improved. The proposed method has been applied for the determination of Tyr in urine and serum samples. Therefore, GO is a powerful catalytic surface for the sensitive and selective determination of Try in biological fluids.