A serine proteinase in the penetration glands of the hexacanths of Hymenolepis diminuta (cestoda, cyclophyllidea)

Abstract

Histochemically demonstrable activity of a serine proteinase was detected in the penetration glands of Hymenolepis diminuta hexacanths. At the optimal pH of 8.4 the enzyme hydrolyzed Af-blocked L-aminoacyl- and N-blocked L-peptidyl-naphthylamides bearing L-arginine at the P₁ subsite. The proteinase did not require either Ca²⁺ or Mg²⁺ for its activity and was insensitive to 1 mM EGTA and 1 mM EDTA. Organic fluorophosphates inhibited it, whereas thiol-blocking compounds did not. At operative pH values of 4.8 and 3.8 generated during electrophoresis in a stacking and a resolving gel, respectively, the proteinase migrated toward the cathode. When examined for proteolytic activity at the optimal pH of 8.4, the separated enzyme produced a single band of gelatinolysis in a gelatin-containing polyacrylamide gel. During in vitro maintenance of the hexacanths, the secretion from their penetration glands formed a mucous cyst surrounding the individual larvae. The cyst was resistant to and protected the hexacanths from the proteolytic activity of trypsin, papain, and proteinases extracted from the gut of the beetle Tenebrio molitor (the host). Hexacanths extracted from the hemocoel of T. molitor at 24 and 48 h after infection were surrounded by similar mucous cysts. Consequently, roles in penetration and protection for the secretion from the penetration glands are postulated.