In situ localization and substrate specificity of earthworm protease-II and protease-III-1 from Eisenia fetida

Recently, the function in fibrinolysis of earthworm proteases has been studied. In our experiments, earthworm protease-II (EfP-II) and earthworm protease-III-1 (EfP-III-1) were isolated and purified from Eisenia fetida. As shown by the assay of sections of the earthworm on fibrin plates, the enzymic activity was mainly detected around the clitellum. In the presence of anti-EfP-II or anti-EfP-III-1 serum, the immunological signals of the two isozymes were clearly found in the anterior alimentary mucosa, suggesting that EfP-II and -III-1 are localized and expressed in intestinal epithelial cells. The Michaelis–Menten constant (Km) for EfP-III-1 reacting with BAEE is smaller (1.7 × 10−5 M) in comparison with the Km values of other substrates such as Chromozym-Try and -TH (3.3 − 6.0 × 10−5 M). This indicates that EfP-III-1 is a trypsin-like protein. EfP-II shows a strong trypsin-like, moderate elastase-like and weak chymotrypsin-like serine function. The relative broad substrate specificity of EfP-II and EfP-III-1 is consistent with their localization in the anterior alimentary canal where different micro-organisms and ingested proteins require to be digested.