Pancreatic chymotrypsin as the essential enzyme for excystation of Eimeria tenella.

Sporocysts from the protozoan parasite, Eimeria tenella, were isolated, preincubated with sodium taurocholate, and treated with various preparations of pancreatic enzymes. Crude trypsin, crude lipase, and purified alpha-chymotrypsin all could break the shells of sporocysts and release sporozoites. Purified trypsin was much less active than crude trypsin and purified lipase showed no activity at all. Specific inhibitors of chymotrypsin, tosyl-L-phenylalanyl chloromethane, diphenylcarbamyl chloride, and chymostatin inhibited the release of sporozoites by all the enzyme samples, whereas tosyl-L-lysyl chloromethane, a specific inhibitor of trypsin, exerted no inhibitory effect. It is thus postulated that chymotrypsin, not trypsin, is an essential enzyme involved in excystation of E. tenella. Purified chymotrypsin is recommended to replace crude trypsin in the vitro excystation of E. tenella as a likely improved procedure.