The effect of gamma irradiation on aqueous solutions of purified bovine fibrinogen has been assessed with reference to clotting properties and physico-chemical changes in the protein. The radiation-induced loss in clottability could be correlated with the unfolding of the protein through cleavage of disulfide linkages. The reconstitution of these bonds could bring about restoration of clotting properties to some extent. The dose-response (0-500 kR) showed initial polymerization and subsequent disintegration of the protein with the formation of insoluble aggregates. An analysis of these revealed that cysteine and methionine residues were oxidized to cysteic acid and methionine sulfone, respectively, at higher doses. The presence of larger amounts of arginine in the aggregates indicated that the precipitation by irradiation was not accompanied by liberation of peptides in the soluble phase, normally observed during the clot formation by action of thrombin. The results show that structural identity of fibrinogen determines its functional integrity as substrate of thrombin.

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