Catalytic properties of cholinesterases: importance of tyrosine 109 in Drosophila protein

Tyrosine 109 in the acetylcholinesterase sequence of Drosopbila melanogaster corresponds to an aspartate in vertebrate cholinesterases. Mutation of this amino acid to a glycine in the human butyrylcholinesterase gives rise to the `atypic‘ phenotype characterized by a reduced activity for charged compounds. We investigated the importance of tyrosine 109 in the Drosopbila sequence by in vitro mutagenesis and its expression in the Xenopus oocyte. We show here that tyrosine 109 contributes to the conformaiton of the active site and the charge of the residue at position 109 is important for catalytic properties. Sensitivity of the enzyme to organophosphorus and carbamatc compounds is modified depending on residues present in position 109, therefore this amino acid is a potential site of resistance for insects to insecticides.