Proteins represent extremely susceptible targets for oxidants. Oxidative modifications of proteins may bring about violation of their structure and functionality. It implies that the structures of proteins are not infallible in terms of their antioxidant defence. The protection mechanisms in preventing oxidative damages for proteins within cells are mainly related to a large variety of antioxidant enzymatic systems. In contrast, plasma proteins are scarcely protected by these systems, so the mechanism that provides their functioning in the conditions of generating reactive oxygen species (ROS) seems to be much more complicated. Oxidation of many proteins was long considered as a random process. However, the highly site-specific oxidation processes was convincingly demonstrated for some proteins, indicating that protein structure could be adapted to oxidation. According to our hypothesis, some of the structural elements present in proteins are capable of scavenging ROS to protect other protein structures against ROS toxicity. Various antioxidant elements (distinct subdomains, domains, regions, and polypeptide chains) may act as ROS interceptors, thus mitigating the ROS action on functionally crucial amino acid residues of proteins. In the review, the oxidative modifications of certain plasma proteins, such as α₂-macroglobulin, serum human albumin, fibrinogen, and fibrin-stabilising factor, which differ drastically in their spatial structures and functions, are analysed. The arguments that demonstrate the possibility of existing hypothetical antioxidant structures are presented. For the first time, the emphasis is being placed on the programmed mechanism of protein oxidation.

Fibrinogen is highly susceptible to oxidation compared to other plasma proteins. Fibrinogen oxidation damages its structure and affects the protein function. Ozone-induced oxidative modifications of the fibrinogen Aα, Bβ, and γ polypeptide chains upon addition of various amounts of the oxidizer were studied by mass spectrometry. Amino acid residues located on all three chains and main structural parts of the protein were revealed to be involved in oxidation. The αC-connector was shown to be most vulnerable to oxidation as compared to other structural parts while E region turned out to be the most protected area of the protein. For the first time, it was established that numerous amino acid residues responsible for the conversion of fibrinogen to fibrin remain unaffected upon fibrinogen oxidation. The data we have obtained in this study indicate that none of the identified residues, which are considered crucial for the binding of both hole “a” and hole “b” to knob “A” and knob “B”, respectively, as well as those responsible for the thrombin binding to fibrinogen E region have been subjected to chemical alterations under moderate oxidation. The data on fibrinogen oxidation acquired in the current study enable one to suppose that some of the structural fibrinogen parts and easily oxidizable residues could be endowed with antioxidant properties. New findings presented here could be essential for detection of adaptive molecular mechanisms capable of mitigating the detrimental action of reactive oxygen species (ROS) on the functioning of oxidatively damaged fibrinogen. Data are available via ProteomeXchange with identifier PXD012046.

Oxidation of fibrinogen with hypochlorite inhibited the fibrin network self-assembly even at the lowest concentration of the oxidant. The analysis of the results of protein electrophoresis at...

N,N-Dimethylformamide (DMF) is often used as a liquid medium for the exfoliation of graphene for further use in a wide range of fields of science and technology: biomedical research, the technology of materials for electronics, and polymer composites. However, the nature of the processes of exfoliation of graphene sheets from the surface of micron-sized graphite particles and the subsequent stabilization of its dispersion has hardly been studied. In this work, the stages of graphene suspension formation in DMF and its mixture with aqua molecules under the action of ultrasonic irradiation were investigated. Characterization of graphene suspensions was carried out using transmission electron microscopy (TEM), dynamic light scattering (DLS), FTIR spectroscopy, Raman spectroscopy, and UV-Vis spectroscopy. The presence of aqua in the colloid system leads to the predominant formation of 3D graphene sheets with larger linear dimensions than in pure DMF. The defectiveness of the basal plane of graphene sheets obtained by exfoliation in pure DMF is significantly lower than in a mixture with aqua, while the edge defectiveness in both cases is rather low. A comprehensive analysis of the spectral data and TEM results with electron diffraction shows that in both cases graphene in suspensions is multilayer. However, if in pure DMF the graphene suspension was formed in one stage and its layering did not exceed five, then in the presence of aqua the formation of the dispersed phase occurred in two stages. At the second stage, a partial association of the sheets from finer fraction increases the sizes of graphene sheets, i.e., the particles with higher surface energy were attached to larger ones or associated with each other. Perhaps this is because aqua molecules included in the complexes and removed from the global hydrogen bond system, tend to restore these bonds and, thus, facilitate the fusion of the smallest and lightest graphene sheets.

The blood coagulation factor XIII (FXIII) plays a critical role in supporting coagulation and fibrinolysis due to both the covalent crosslinking of fibrin polymers, rendering them resistant to plasmin lysis, and the crosslinking of fibrin to proteins of the fibrinolytic system. The hypochlorite-mediated oxidation of the blood coagulation factor XIII (FXIII) at the different stages of its enzymatic activation is studied for the first time in this paper. The consolidated results obtained with the aid of MS/MS, electrophoresis, and colorimetry demonstrate that in the process of FXIII’s conversion into FXIIIa, the vulnerability of FXIII to hypochlorite-induced oxidation increased as follows: native FXIII < FXIII + Ca²⁺ << FXIII + Ca²⁺/thrombin. The modification sites were detected among all the structural regions of the catalytic FXIII-A subunit, except for the activation peptide, and embraced several sushi domains of the FXIII-B subunit. Oxidized amino acid residues belonging to FXIII-A are surface-exposed residues and can perform an antioxidant role. The regulatory FXIII-B subunits additionally contribute to the antioxidant defense of the catalytic center of the FXIII-A subunits. Taken together, the present data along with the data from previous studies demonstrate that the FXIII proenzyme structure is adapted to oxidation.

The development of various enzyme-linked immunosorbent assays (ELISAs) coupled with surface-enhanced Raman scattering (SERS) detection is a growing area in analytical chemistry due to their potentially high sensitivity. A SERS-based ELISA with horseradish peroxidase (HRP) as an enzymatic label, an o-phenylenediamine (oPD) substrate, and a 2,3-diaminophenazine (DAP) enzymatic product was one of the first examples of such a system. However, the full capabilities of this long-known approach have yet to be revealed. The current study addresses a previously unrecognized problem of SERS detection stage performance. Using silver nanoparticles and model mixtures of oPD and DAP, the effects of the pH, the concentration of the aggregating agent, and the particle surface chloride stabilizer were extensively evaluated. At the optimal mildly acidic pH of 3, a 0.93 to 1 M citrate buffer, and AgNPs stabilized with 20 mM chloride, a two orders of magnitude advantage in the limits of detection (LODs) for SERS compared to colorimetry was demonstrated for both DAP and HRP. The resulting LOD for HRP of 0.067 pmol/L (1.3 amol per assay) underscores that the developed approach is a highly sensitive technique. We suppose that this improved detection system could become a useful tool for the development of SERS-based ELISA protocols.