Ozone-induced oxidative modification of plasma fibrin-stabilizing factor.

The plasma fibrin-stabilizing factor (pFXIII) function is to maintain a hemostasis by the fibrin clot stabilization. The conversion of pFXIII to the active form of the enzyme (FXIIIа) is a multistage process. Ozone-induced oxidation of pFXIII has been investigated at different stages of its enzyme activation. The biochemical results point to a decrease of an enzymatic activity of FXIIIа depending largely on the stage of the pFXIII conversion into FXIIIа at which oxidation was carried out. UV-, FTIR- and Raman spectroscopy demonstrated that chemical transformation of cyclic, NH, SH and S-S groups mainly determines the oxidation of amino acid residues of pFXIII polypeptide chains. Conversion of pFXIII to FXIIIa proved to increase protein sensitivity to oxidation in the order: pFXIII<pFXIII activated by thrombin<pFXIII in the presence of calcium ions<FXIIIa. The dynamic light scattering data indicate that the three-dimensional structure of pFXIII becomes loosened due to oxidative modification. ESR spectroscopy data also point to conformational changes of the fibrin-stabilizing factor under oxidation. Taking into account these new findings it seems reasonable to assume that the inhibitory/carrier FXIII-B subunits can serve as scavengers of ROS. Hypothetically, this mechanism could help to protect the key amino acid residues of the FXIII-A subunits responsible for the enzymatic function of FXIIIa.