Molecular Properties of Drosophila Acetylcholinesterase

Abstract

Two distinct classes of acetylcholinesterase (AChE) from the fruit fly D. melanogaster are reported: a solbule species that shows heterogeneity of forms; and a particulate species. The subunit composition of the particulate enzyme was studied using the active site label [3H]diisopropylfuorophosphate. Comparison of the electrophoretic patterns on nondenaturing gels using the activity stain and the active site label shows that the label is specific to AChE. The smallest active site-containing subunit of the enzyme is a monomer of .apprx. 60,000 daltons MW. Two such units are linked by disulfide bonds to produce a dimer of about 110,000 daltons. Another monomeric form of MW .apprx. 64,000 daltons, although present, does not participate in the dimerization. The particulate enzyme when solubilized exists as a 9-10S species as determined by sucrose gradient centrifugation. This species has a MW > 200,000, as shown by its behavior on a coarse-bead Sephadex-G200 column. Electrophoretic analysis suggests a MW of nearly 250,000 daltons for this form. This species is likely to be a tetramer. One possibility is that this tetramer is made up of 2 units of 64,000 daltons each and a dimer of 110,000 daltons. Preliminary data on mutant enzymes that support such a possibility are also presented.