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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 α-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.

The mechanism of self-assembly of fibrin monomers and fibrinogen aggregation during ozone oxidation has been studied by the methods of elastic and dynamic light-scattering and viscosimetry. Fibrin obtained from oxidized fibrinogen exhibits higher average fiber mass/length ratio compared with native fibrin. Fibrinogen ozonation sharply reduced the latent period preceding aggregation of protein molecules; however, the mechanism of self-assembly of ozonated and non-ozonated fibrinogen cluster was identical. In both cases flexible polymers are formed and reaching a certain critical length they form densely packed structures and aggregate. Using infrared spectroscopy, it has been shown that free radical oxidation of amino acid residues of fibrinogen polypeptide chains catalyzed by ozone results in formation of carbonyl, hydroxyl, and ether groups. It is concluded that fibrinogen peripheral D-domains are the most sensitive to ozonation, which causes local conformational changes in them. On one hand, these changes inhibit the reaction of longitudinal polymerization of monomeric fibrin molecules; on the other hand, they expose reaction centers responsible for self-assembly of fibrinogen clusters.

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