Acetylcholinesterase (AChE) is an enzyme broadly
distributed in many species, including parasites. It occurs
in multiple molecular forms that differ in their quaternary
structure and mode of anchoring to the cell surface. This
review summarizes biochemical and immunological investigations
carried out in our laboratories on AChE of the helmint,
Schistosoma mansoni. AChE appears in S. mansoni
in two principal molecular forms, both globular, with sedimentation
coefficients of ∼6.5 and 8 S. On the basis of their
substrate specificity and sensitivity to inhibitors, both
are “true” acetylcholinesterases. Approximately
half of the AChE activity of S. mansoni is located
on the outer surface of the parasite, attached to the tegumental
membrane via a covalently attached glycosylphosphatidylinositol
anchor. The remainder is located within the parasite, mainly
associated with muscle tissue. Whereas the internal enzyme
is most likely involved in termination of neurotransmission
at cholinergic synapses, the role of the surface enzyme
remains to be established; there are, however, indications
that it is involved in signal transduction. The two forms
of AChE differ in their heparin-binding properties, only
the internal 8 S form of the AChE being retained on a heparin
column. The two forms differ also in their immunological
specificity, since they are selectively recognized by different
monoclonal antibodies. Polyclonal antibodies raised against
S. mansoni AChE purified by affinity chromatography
are specific for the parasite AChE, reacting with both
molecular forms, but do not recognize AChE from other species.
They interact with the surface-localized enzyme on the
intact organism, and produce almost total complement-dependent
killing of the parasite. S. mansoni AChE is thus
demonstrated to be a functional protein, involved in multifaceted
activities, which can serve as a suitable candidate for
diagnostic purposes, vaccine development, and drug design.