Nippostrongylus brasiliensis:Characterisation of a Somatic Amphiphilic Acetylcholinesterase with Properties Distinct from the Secreted Enzymes

Abstract

Hussein, A. S., Grigg, M. E., and Selkirk, M. E. 1999.Nippostrongylus brasiliensis:Characterisation of a somatic amphiphilic acetylcholinesterase with properties distinct from the secreted enzymes.Experimental Parasitology91, 144–150. We have previously determined thatNippostrongylus brasiliensissecretes three monomeric nonamphiphilic (Gna1) variants of acetylcholinesterase (AChE) with broadly similar properties. In this study we have examined AChE expression in somatic extracts ofN. brasiliensisand report the identification of an additional enzyme which is not secreted. The enzyme was resolved by sucrose density gradient centrifugation with a sedimentation coefficient of 10.2 S which was shifted to 9.4 S in the presence of Triton X-100, identifying the enzyme as a tetrameric amphiphilic (Ga4) form. The amphiphilic properties of this enzyme were confirmed by charge-shift electrophoresis, in which migration was accelerated by interaction with sodium deoxycholate. The enzyme showed low activity with butyrylthiocholine, and a Michaelis constant of 91 ± 13 μM for acetylthiocholine was determined. It was highly sensitive to the AChE- specific inhibitor bis (4-allyldimethylammoniumphenyl)pentan-3-one dibromide, with an IC50of 6.5 ± 0.4 μM, but was also inhibited by the butyrylcholinesterase-specific inhibitor tetramonoisopropylpyrophosphortetramide, albeit with a higher IC50of 46.5 ± 6.1 μM. This enzyme can therefore be distinguished from the secreted AChEs by its amphiphilic properties, sedimentation in sucrose gradients, and sensitivity to cholinesterase inhibitors.