Taenia saginata oncosphere excretory/secretory peptidases.

To identify oncosphere excretory/secretory peptidases, Taenia saginata adult worms were collected from 3 patients. Eggs were hatched and activated in vitro and oncospheres cultured in vitro. The culture medium from the oncospheres was assayed with peptide substrates coupled to 7-amino-4-trifluoromethyl coumarin (AFC), and free AFC was detected fluorometrically. The endopeptidase substrates Z-Phe-Arg-AFC and Z-Arg-AFC as well as the aminopeptidase substrate Arg-AFC were hydrolyzed when incubated with spent media from the oncospheres compared to control culture medium removed prior to incubation. Hydrolysis of Z-Phe-Arg-AFC was inhibited 78% by preincubation of the medium with the serine proteinase inhibitor Phenylmethylsulfonyl fluoride. Endopeptidase activity was partially enhanced in the presence of exogenous thiols and partially inhibited with the cysteine proteinase inhibitor E-64, suggesting the presence of both serine and cysteine endopeptidases. No significant inhibition was noted with pepstatin or phenanthroline. The peptidase activities detected with Z-Phe-Arg-AFC and Arg-AFC were separated by gel-filtration fast protein liquid chromatography and eluted at volumes corresponding to molecular weights of 18 and 30 kDa, respectively. These data demonstrate that T. saginata oncospheres produce excretory/secretory peptidases, including serine and cysteine endopeptidases and an aminopeptidase. These enzymes may play a role in invasion of the intestinal mucosa of the intermediate host.