Native molecular forms of head acetylcholinesterase from adult Drosophila melanogaster: quaternary structure and hydrophobic character.

The native molecular forms of acetylcholinesterase (AChE) present in adult Drosophila heads were characterized by sedimentation analysis in sucrose gradients and by nondenaturing electrophoresis. The hydrophobic properties of AChE forms were studied by comparing their migration in the presence of Triton X100, 10-oleyl ether, or sodium deoxycholate, or in the absence of detergent. We examined the polymeric structure of AChE forms by disulfide bridge reduction. We found that the major native molecular form is an amphiphilic dimer which is converted into hydrophilic dimer and monomer on autolysis of the extracts, or into a catalytically active amphiphilic monomer by partial reduction. The latter component exists only as trace amounts in the native enzyme. Two additional minor native forms were identified as hydrophilic dimer and monomer. Although a significant proportion of AChE was only solubilized in high salt, following extractions in low salt, this high salt-soluble fraction contained the same molecular forms as the low salt-soluble fractions: thus, we did not detect any molecular form resembling the asymmetric forms of vertebrate cholinesterases.