Trichinella spiralis: proteinases in the larvae

Under in vitro conditions, muscle larvae of Trichinella spiralis secreted m inute amounts of a cysteine proteinase into the outer environment from the stichosome. The proteinase hydrolyzed azocoll at pH 5.0 but not a number of synthetic N-blocked and N-unsubstituted proteinase substrates at this pH. The reducing compound dithioerythritol enhanced the enzyme activity, but th e thiol-blocking reagent sodium-p-hydroxymercuribenzoate (0.1 mM) was witho ut effect. Phenylmethylsulfonyl fluoride (PMSF) (2 mM) and leupeptin (100 m M) produced partial and complete inhibition, respectively, whereas soybean trypsin inhibitor, pepstatin A, and 1,10-phenanthroline were non-inhibitory . Calcium (1 mM) produced a slight decrease in the activity that was revers ed by 1 mM EGTA. Although multiple proteinase activities were detected hist ochemically in the somatic muscles, stichosome, midgut, and genital primord ium of the muscle larvae, none of these enzymes appeared to be the one secr eted. Several histochemically demonstrable proteinases were also found in t he cells of 48- to 72-h-old juveniles of the parasite. One was localized in the esophageal lumen and at or around the anterior esophagus of the larvae , where developing stichocytes are believed to occur. The proteinase hydrol yzed N-acetyl-L-methionine-1-naphthyl eater and was sensitive to the metal cation-complexing compound EGTA as well as to PMSF, an inhibitor of serine proteinases.