We analyzed the molecular forms of acetylcholinesterase (AChE) in the nematode Steinernema carpocapsae. Two major AChEs are involved in acetylcholine hydrolysis. The first class of AChE is highly sensitive to eserine = 0.05 pM). The corresponding molecular forms are: an amphiphilic 14s form converted into a hydrophilic 14.5s form by mild proteolysis and two hydrophilic 12s and 7s forms. Reduction of the amphiphilic 14s form with 10 mM dithiothreitol produces hydrophilic 7s and 4s forms, indicating that it is an oligomer of hydrophilic catalytic subunits linked by disulfide bond(s) to a hydrophobic structural element that confers the amphiphilicity to the complex. Sedimentation coefficients suggest that 4S, 7S, 12s forms correspond to hydrophilic monomer, dimer, tetramer and that the 14s form is also a tetramer linked to one structural element. The second class of AChE is less sensitive to eserine (IC50 =0.1 mM). Corresponding molecular forms are hydrophilic and amphiphilic 4s forms (monomers) and a major amphiphilic 7s form converted into a hydrophilic dimer by Bacillus thuringiensis phosphatidylinositol-specific phospholipase C. This amphiphilic 7s form thus possesses a glycolipid anchor. It appears that Steinernemu (a very primitive invertebrate) presents AChEs with two types of membrane association that closely resemble those described for amphiphilic G2 and G4 forms of AChE in more evolved animals.Acetylcholinesterase (AChE) and butyrylcholinesterase are highly polymorphic enzymes in vertebrates. Six different molecular forms can be expressed in a tissue-specific and agedependent manner. Three globular forms (Gl, G2 and G4 forms) correspond to monomers, dimers and tetramers of catalytic subunits, and three asymmetric forms (A forms) are associations of one, two or three tetramers to a collagen 'tail' [I].In invertebrates, only AChE has been described so far and its molecular diversity is more restricted : for example, there is no convincing evidence for the existence of collagen-tailed, asymmetric forms in these organisms. In insects, only G1 and G 2 forms have been characterized. The major molecular form is an amphiphilic dimer (2, 31 linked to the plasma membrane by a glycolipid anchor [4 -61. A glycolipid-anchored AChE has also been characterized in the trematode Schistosoma mansoni [7].
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