TARGET SIZE ANALYSIS OF AN AVERMECTIN BINDING-SITE FROM DROSOPHILA-MELANOGASTER

A high-affinity avermectin binding site from Drosophila melanogaster h ead membranes was subjected to target size analysis by radiation inact ivation in order to determine the functional unit size. Using the [H-3 ]ivermectin binding assay to assess ligand binding activity, the targe t size was determined to be 44.3+/-3.9 kDa, This result suggests that the size of the functional unit required for high-affinity ligand bind ing is a monomer. The membrane-associated acetylcholinesterase present in the Drosophila head membranes was also analyzed by radiation inact ivation and served as a control. By monitoring enzymatic activity, the functional unit size of the Drosophila acetylcholinesterase was deter mined to be 70+/-9.7 kDa. This corresponds to the molecular weight of a dimer composed of a 55 kDa subunit and a 16-18 kDa subunit.