Purification and biochemical characterization of a fibrinolytic enzyme from Bacillus subtilis BK-17

A fibrinolytic enzyme from Bacillus subtilis BK-17 has been purified to homogeneity by gel-filtration and ion-exchange chromatography. Compared to the crude enzyme extract, the specific activity of the enzyme increased 929-fold with a recovery of 29%. The subunit molecular mass of the purified enzyme was estimated to be 31 kDa by SDS–PAGE. The N-terminal amino acid sequence of the purified fibrinolytic enzyme was: A-Q-S-V-P-Y-G-V-S-Q-I-K-A-P-A-A-H-N. The sequence was highly homologous to the fibrinolytic enzymes nattokinase, subtilisin J and subtilisin E from Bacillus spp. However, there was a substitution of three amino acid residues in the N-terminal sequence. The amidolytic activity of the purified enzyme for several substrates was assessed. In comparison with nattokinase and CK (fibrinolytic enzyme from a Bacillus spp.), which showed strong fibrinolytic activity, the amidolytic activity of the enzyme for the synthetic substrate, kallikrein (H-D-Val-Leu-Arg-pNA, S-2266) increased 2.4- and 11.8-fold, respectively.