THE AMOUNT OF ACETYLCHOLINESTERASE ON THE PARASITE SURFACE REFLECTS THE DIFFERENTIAL SENSITIVITY OF SCHISTOSOME SPECIES TO METRIFONATE

Acetylcholinesterase (AChE) is present in all stages of the life-cycle of schistosomes and is located in muscle and on the surface of the pa rasite. Metrifonate is a drug that inhibits AChE. We compared the AChE s from three schistosome species (Schistosoma mansoni, Schistosoma hae matobium and Schistosoma bovis) that have different susceptibilities t o metrifonate in vivo. Sensitivities to AChE inhibitors were similar. The subunits of AChE were 110 kDa and 76 kDa and the dominant molecula r form of AChE was a G2 form in all three species. This was the major form on the tegument while additional molecular forms were associated with the internal tissues. Differences in relative amounts of AChE act ivity between these species were found in the adults but not in the sc histosomula. At the adult stage the major difference between species l ay in the relative amounts of AChE activity in their teguments. S. hae matobium teguments carried 20 times and S. bovis 6.9 times the activit y present on S. mansoni teguments. These quantitative differences asso ciate with the relative sensitivities of these species to metrifonate.