THE ROLE OF THE SHEATH IN RESISTANCE OF HAEMONCHUS-CONTORTUS INFECTIVE-STAGE LARVAE TO PROTEOLYTIC DIGESTION

Surface iodinated larvae of Haemonchus contortus were incubated in the presence of the fungal protease, proteinase K, and proteolysis quanti fied by scintillation counting of released radioactivity. No radioacti vity was released from live ensheathed infective-stage larvae (L(3(2m) )). In contrast, 58% of the radioactivity was released from ecdysed, s econd molt (2M) cuticles (sheaths) of L(3(2M)) and 48% from live exshe athed third-stage larvae (L(3)). When L(3(2M)) larvae were killed by h eat (80 degrees C for 10 min) prior to proteinase K incubation, 61% of the radioactivity was released, whereas less than 7% was released fro m larvae killed by the metabolic inhibitors NaN3 or KCN. Proteinase K released 44% of the radioactivity from live L(3(2M)) larvae which had been preincubated with 1% sodium dodecylsulfate (SDS), whereas no radi oactivity was released from L(3(2M)) larvae preincubated with either 1 % Triton X-100, 0.2% CTAB, 50% methanol, 50% ethanol, or water. Follow ing incubation with proteinase K, only L(3(2M)) larvae which had been heat-killed or preincubated with SDS showed visible damage to the shea th. Material released from L(3(2M)) larvae by exposure to either heat or SDS contained a 98000 M(r) protein by SDS-PAGE L autoradiography. T hese results indicate that viable L(3(2M)) larvae are resistant to att ack by proteinase K and that this resistance is dependent on structura l properties of the sheath.