[Modification of functional groups of the streptokinase molecule during photooxidation].

Photochemical oxidation with methylene blue as photosensitizer results in the destruction of one histidine residue in the streptokinase molecule. This process is characterized by the rate constant corresponding to the modification of free L-histidine and results in partial inactivation of the protein. The rate of protein photo oxidation and photoinactivation is pH-dependent. As can be judged from the results of CD spectroscopy and gel chromatography, in weakly acidic (but not in weakly alkaline) media the reaction results in conformation changes of the streptokinase globule which affect the state of the protein tryptophanyl residue. It was found that the imidazole group destroyed during the photooxidation reaction is not essential either for the specific activity of streptokinase or for the formation of is stable complex with human plasminogen. The specificity of modification of the streptokinase histidine residue during the photooxidation reaction is discussed.