Ligula intestinalis (Cestoda: Pseudophyllidae): Studies on the properties of proteolytic and protease inhibitor activities of plerocercoid larvae

The somatic extract of L. intestinalis plerocercoids reveals hydrolytic activity against N-Benzoyl-l-tyrosine ethyl ester (BTEE) and Azocoll, and inactivates the esterolysis by mammalian trypsin and chymotripsin. The proteolytic enzyme activity and the inhibitory effect were completely separated by Sephadex G-100 column chromatography. Gel chromatography of the somatic extract revealed two peaks of proteolytic activity : one is bound to macromolecular substances, the other appears to be in free form and has a molecular weight of approx 60,000–65,000. The proteolytic activity showed the following characteristics : Tris-HCl buffer provided the highest activity against BTEE, the pH optimum was 7·4–7·8; the enzyme was activated by 10^?5m-Ca²⁺, Mg²⁺ or Mn²⁺, it was inhibited by 10^?5m-Cu²⁺, but not by 10^?5m-Zn²⁺. 0.001% soybean trypsin inhibitor, 2 × 10^?3m-EDTA, 1 mm-tosyl-l-phenylalanyl chloromethane, 1000 KIU/ml Trasylol did not inhibit the proteolytic activity, but it was inhibited by 1 mm-phenylmethyl-sulphonyl fluoride. The enzyme activity completely ceased upon 5 % TCA treatment or incubation at 56°C for 30 min. The trypsin and chyrnotrypsin inhibitor activities were eluted from the Sephadex G-100 column in a single peak with an estimated molecular weight of 6700–7200. The inhibitory effect was not sensitive to pH changes, and treatment by 5% TCA or incubation at 80°C for 15 min was ineffective. The proteolytic activity of plerocercoid extract was not effected ‘in vitro’ by the inhibitors isolated from this parasite.