Tyrosine Dimer Research Articles

Водородные связи в молекулярных кристаллах аланина и тирозина: NBO анализ

At present, the theoretical concepts of the hydrogen bond (H-bond) in condensed media, for example, in living systems, biomolecules, are not fully solved. Quantum chemical modeling is used as one of the methods for studying the nature and determining the strength of the H-bond. In this paper, we continue to study the system of hydrogen bonds in molecular crystals of alanine and tyrosine. The dimers of these amino acids were modeled using the DFT method using the B97D functional with bases 6-31++G**. In the framework of NBO analysis, the stabilization energies of the formed hydrogen bond and the value of the transferred charge are calculated. It is shown that in alanine dimers, the main factor affecting the h-bond stabilization energy is the geometric parameters and, first of all, (N-H...O). The binding σ-orbital of the hydrogen bond is the result of the interaction of a hybrid NBO of the lone electron pairs of an oxygen atom and a loosening σ*-NBO N−H bond. The nature of bond formation in all three cases is the same, and the charge transfer value is greater than the value of the bond criterion, which indicates the presence of hydrogen bonds in all analyzed alanine systems. In tyrosine dimers, two H-bonds are formed that are similar in nature, as well as in geometric and energy parameters. The third H-bond is very weak, and the amount of charge transfer indicates its absence. The main interaction between the molecules in the third tyrosine dimer is the H-bond between the –СОО− and –OH groups. It was found that the scheme of formation of hydrogen bonds in molecular crystals of tyrosine is somewhat different from that of alanine.

Photochemistry of tyrosine dimer: when an oxidative lesion of proteins is able to photoinduce further damage.

The tyrosine dimer (Tyr2), a covalent bond between two tyrosines (Tyr), is one of the most important modifications of the oxidative damage of proteins. This compound is increasingly used as a marker of aging, stress and pathogenesis. At physiological pH, Tyr2 is able to absorb radiation at wavelengths significantly present in the solar radiation and artificial sources of light. As a result, when Tyr2 is formed in vivo, a new chromophore appears in the proteins. Despite the biomedical importance of Tyr2, the information of its photochemical properties is limited due to the drawbacks of its synthesis. Therefore, in this work we demonstrate that at physiological pH, Tyr2 undergoes oxidation upon UV excitation yielding different products which conserve the dimeric structure. During its photodegradation different reactive oxygen species, like hydrogen peroxide, superoxide anion and singlet oxygen, are produced. Otherwise, we demonstrated that Tyr2 is able to sensitize the photodegradation of tyrosine. The results presented in this work confirm that Tyr2 can act as a potential photosensitizer, contributing to the harmful effects of UV-A radiation on biological systems.

Study on the Effect of Several Natural Products on Tyrosine Damage Induced by Peroxynitrite

Peroxynitrite (ONOO^ˉ), a powerful oxidant, is produced by nitric oxide (NO.) and superoxide anion (O₂.^ˉ). Under the physiological condition, the ONOO^ˉ could oxidize the lipids, nitrifyproteins, damage DNA and others biomolecules, thereby harm human health. The study used natural products Capsanthin, Myricetin and Capsaicin as the research object and controlled with Vc, and developed the method of HPLC-DAD to separate the components of nitrification damage system, which could determine the inhibition rate of natural products on the formation of 3-nitrotyrosine (3-NT). The fluorescence spectrometry was employed to determine the ability of these substances to inhibit tyrosine dimer and inhibit the self-oxidation of phthalate. The results showed that Capsanthin, Myricetin and Capsaicin had strong inhibitory effect on the generation capacity of 3-NT and tyrosine dimer, and strong inhibitory effect on the self-oxidation of phthalate.

New poly(ester-amide) copolymers modified with polyether (PEAE) for anticancer drug encapsulation

New poly(ester–amide) copolymers modified with polyethers were developed for carboplatin encapsulation. These new copolymers contain hydrophobic blocks made of tyrosine derivative and dimer fatty acid, and poly(ethylene glycol) (PEG) as hydrophilic blocks. Short-term hydrolytic degradation revealed high water absorption, slight increase of pH of simulated body fluid and change of sample shape, which indicated the erosive mechanism of polymers degradation. Poly(ester-amide)-PEG copolymers were used for microspheres preparation and carboplatin encapsulation. A double emulsification process was used to produce microspheres with an average diameter of 20–30 μm. It was found that the amount of drug released was controlled by the molecular mass of PEG used for microspheres preparation. Mathematical models were used to elucidate the release mechanism of the carboplatin from the microspheres. The results demonstrate that poly(ester-amide)-PEG copolymers may be used for targeted carboplatin encapsulation and release.

Energetics of Direct and Water-Mediated Proton-Coupled Electron Transfer

Proton-coupled electron transfer (PCET) is an elementary chemical reaction crucial for biological oxidoreduction. We perform quantum chemical calculations to study the direct and water-mediated PCET between two stacked tyrosines, TyrO(•) + TyrOH → TyrOH + TyrO(•), to mimic a key step in the catalytic reaction of class Ia ribonucleotide reductase (RNR). The energy surfaces of electronic ground and excited states are separated by a large gap of ~20 kcal mol(-1), indicative of an electronically adiabatic transfer mechanism. In response to chemical substitutions of the proton donor, the energy of the transition state for direct PCET shifts by exactly half of the change in energetic driving force, resulting in a linear free energy relation with a Brønsted slope of ½. In contrast, for water-mediated PCET, we observe integer Brønsted slopes of 1 and 0 for proton acceptor and donor modifications, respectively. Our calculations suggest that the π-stacking of the tyrosine dimer in RNR results in strong electronic coupling and adiabatic PCET. Water participation in the PCET can be identified perturbatively in a Brønsted analysis.

A novel immobilization multienzyme glucose fluorescence capillary biosensor

Based on the immobilization enzyme technology and the fluorescence capillary analysis method, the authors have developed a highly sensitive fluorescence reaction system and a novel immobilization multienzyme glucose fluorescence capillary biosensor for determining glucose contents. Reaction principle of the system is that under the catalysis of glucose oxidase (GOD) and horseradish peroxidase (HRP) immobilized on inner surface of a medical capillary, β- d-glucose reacts with dissolved oxygen to form gluconic acid-δ-lactone and hydrogen peroxide, and then the latter reacts with l-tyrosine to produce a tyrosine dimer, which has maximal excitation and emission wavelengths at 320 nm and 410 nm, respectively. Fluorescence of the dimer is proportional to the concentration of the β- d-glucose. Optimization conditions suitable for the reaction system and the biosensor were as follows. Concentration of the l-tyrosine used as fluorescence reagent was 0.15 mol L −1, the active concentrations of the GOD and the HRP for the immobilization were 15 kU L −1 and 8 kU L −1, respectively. Consumptions of the sample and reagents in one determination were 5.0 μL and 15 μL, respectively. Quantitative range of the biosensor for the glucose was in the range 1–10 μmol L −1, its relative standard deviation was less than 4.9%, and its detection limit was 0.62 μmol L −1. The biosensor's recovery was in the range 96–105%. Results of some serum determined with the biosensor and with a commercial glucose-kit were well coincident to each other. Accordingly, the biosensor can be applied to the determination of serum glucose contents in the diagnosis of diabetes.

Identification of oxidation products and free radicals of tryptophan by mass spectrometry

New oxidation products and free radicals derived from tryptophan (Trp) oxidation under Fenton reaction conditions were identified using mass spectrometry. After the oxidation of tryptophan using hydrogen peroxide and iron (II) system (Fenton reaction), mono- and dihydoxy tryptophans and N-formylkynurenine were identified using electrospray mass spectrometry (ES-MS) and ES-MS/MS. Besides these products, new products resulting from the reaction of tryptophan and oxidized tryptophan and 3-methyl indole derivatives were also identified. The 3-methyl indole derivatives resulted, most probably, from the oxidation process and not from in-source processes. A dimer formed by cross-linking between two Trp radicals (Trp-Trp), similar to the previously described tyrosine dimer was observed, as well as the corresponding monohydroxy-dimer (Trp-Trp-OH). Tandem mass spectrometry was used to identify the structures of these new oxidation products. Free radicals derived from tryptophan oxidation under Fenton reaction were detected using as spin trap the DMPO. The free radical species originated during the oxidation reaction formed stable adducts with the spin trap, and these adducts were identified by ES-MS. New adducts of oxidized tryptophan radicals, namely monohydroxy-tryptophan and dihydroxy-Trp dimer radicals, with one and two DMPO spin trap molecules where identified. Tandem mass spectrometry was used to confirm the proposed structure of the observed adducts.

Conformational analysis of poly(L-tyrosine) and tyrosyl oligomers based on backbone circular dichroism spectra obtained by fluorescence-detected circular dichroism

The conformational analysis of tyrosyl compounds based on their backbone circular dichroism (CD) spectra was performed. The separation of the backbone CD component of the tyrosyl compounds from natural CD was achieved by fluorescence-detected circular dichroism (FDCD) spectroscopy. The backbone CD spectrum of poly(L-tyrosine) (PLT) in methanol showed two negative extrema at 213 and 222 nm. The solution conformation of PLT was concluded to be the α-helix conformation. The conformational transition of PLT from the α-helix conformation to the β structure was caused by the addition of an aqueous sodium hydroxide solution to the PLT methanol solution. A steep conformational transition was observed within the sodium hydroxide concentration range of 3 × 10−3 to 5 × 10−3 M. The origin of the positive CD band of the tyrosyl compounds near the amide n−π* transition band was experimentally revealed by applying the FDCD method to N-acetyl-L-tyrosinamide, which is a monomer model compound of PLT. The observed CD of N-acetyl-L-tyrosinamide was attributed to the optical rotation coming from the La transition of the phenolic ring on the side chain. N-acetyl-L-tyrosinamide had no backbone CD band in the amide n−π* transition region, whereas the tyrosine dimer, tyrosine trimer, and tyrosine hexamer showed a positive dichroic band derived from the optical activity of their backbone amide chromophores at around 230 nm. The tyrosyl compounds made up of two or more tyrosine residues adopted specific configurations. © 1997 John Wiley & Sons, Inc. Biospect 3: 103–111, 1997

Structure of a hydroxyl radical induced cross-link of thymine and tyrosine.

DNA-protein cross-links are formed when living cells or isolated chromatin is exposed to ionizing radiation. Little is known about the actual cross-linked products of DNA and proteins. In this work, a novel hydroxyl radical induced cross-link of thymine and tyrosine has been isolated along with a tyrosine dimer by high-performance liquid chromatography of aqueous mixtures of tyrosine and thymine that had been exposed to hydroxyl radicals generated by ionizing radiation. The isolated compounds have been examined by gas chromatography-mass spectrometry, high-resolution mass spectrometry, and 1H and 13C nuclear magnetic resonance spectroscopy. The structure of the thymine-tyrosine cross-link has been identified as the product from the formation of a covalent bond between the methyl group of the thymine and carbon 3 of the tyrosine ring. In addition, the 3,3' tyrosine dimer was isolated and characterized. The mechanism of the formation of these compounds is discussed. This work presents the first complete chemical characterization of a hydroxyl radical induced DNA base-amino acid cross-link.

The peroxidase-catalyzed oxidation of tyrosine

The horseradish peroxidase- and lactoperoxidase-(donor: H 2O 2 oxidoreductase, EC 1.11.1.7) catalyzed oxidation of tyrosine has been studied. Kinetics of the oxidation catalyzed by these enzymes were followed both spectrophotometrically and fluorometrically. Oxidation of tyrosine by both enzymes has a pH optimum at 8.2. Most interesting was the finding that both enzymes demonstrate stereospecificity in the oxidative coupling reaction for tyrosine isomers. Lactoperoxidase couples the l-isomer more readily than the d-isomer, in contrast horseradish peroxidase oxidizes the d-isomer more readily. The apparent second order rate constants for lactoperoxidase catalyzed oxidation are 1.03·10 4 M −1·s −1 for l-tyrosine and 6.89·10 3 M −1·s −1 for d-tyrosine. The values for horseradish peroxidase are 7.53·10 2 M −1·s −1 for l-tyrosine and 1.55·10 3 M −1·s −1 for d-tyrosine. The products of these enzyme-catalyzed reactions were characterized by chromatographic, spectral and fluorimetric analysis. The product formed under the initial rate conditions was the tyrosine dimer linked in o, o-biphenyl linkage. Extensive oxidation results in the production of trityrosine, thyronine and insoluble yellow to brown colored products.