Purification and characterization of a cholinesterase from Haemonchus contortus

Acetylcholinesterase (AChE) was purified from the extract of adult Haemonch us contortus by gel filtration, ion-exchange and ConA-Sepharose chromatogra phy. The enzyme was also found to be secreted by the parasite during in vit ro cultivation which was partially purified from the excretory-secretory pr oducts. Presence of enzyme specific antibodies were observed in animals hav ing H. contortus infection. The molecular mass of the enzyme by SDS-PAGE wa s 144 kDa. The enzyme showed typical Michaelis-Menten kinetics at low subst rate concentrations but was inhibited by substrate concentrations greater t han 4 mM. The enzyme was stable at 4 degreesC for several weeks but lost 60 % of the activity when heated to 60 degreesC for 5 min. Physostigmine and n eostigmine inhibited enzyme activity at low (muM) concentrations whereas ph enyl methyl sulfonyl fluoride (PMSF) and sodium fluoride (NaF) inhibited on ly at high concentrations (mM). Significance of secreted AChE in host-paras ite relationship is discussed.