A novel proteolytic enzyme with fibrinolytic activity， FSP3， was purified from the recently isolated Streptomyces sp. P3， which is a novel bacterial strain isolated from soil. FSP3 was purified to electrophoretic homogeneity by ammonium sulfate precipitation， anion exchange， and gel filtration. FSP3 is considered to be a single peptide chain with a molecular mass of 44 kDa. The maximum activity of the enzyme was observed at 50°C and pH 6.5， and the enzyme was stable between pH 6 and 8 and below 40°C. In a fibrin plate assay， FSP3 showed more potent fibrinolytic activity than urokinase， which is a clinical thrombolytic agent acting as a plasminogen activitor. The activity was strongly inhibited... More
A novel proteolytic enzyme with fibrinolytic activity， FSP3， was purified from the recently isolated Streptomyces sp. P3， which is a novel bacterial strain isolated from soil. FSP3 was purified to electrophoretic homogeneity by ammonium sulfate precipitation， anion exchange， and gel filtration. FSP3 is considered to be a single peptide chain with a molecular mass of 44 kDa. The maximum activity of the enzyme was observed at 50°C and pH 6.5， and the enzyme was stable between pH 6 and 8 and below 40°C. In a fibrin plate assay， FSP3 showed more potent fibrinolytic activity than urokinase， which is a clinical thrombolytic agent acting as a plasminogen activitor. The activity was strongly inhibited by the serine protease inhibitor PMSF， indicating that it is a serine protease. Additionally， metal ions showed different effects on the activity. It was significantly suppressed by Mg(2+) and Ca(2+) and completely inhibited by Cu(2+)， but slightly enhanced by Fe(2+). According to LC-MS/MS results， its partial amino acid sequences are significantly dissimilar from those of previously reported fibrinolytic enzymes. The sequence of a DNA fragment encoding FSP3 contained an open reading frame of 1287 base pairs encoding 428 amino acids. FSP3 is a bifunctional enzyme in nature. It hydrolyzes the fibrin directly and activates plasminogen， which may reduce the occurrence of side effects. These results suggest that FSP3 is a novel serine protease with potential applications in thrombolytic therapy.
