MOLECULAR DISSECTION OF CHOLINESTERASE DOMAINS RESPONSIBLE FOR CARBAMATE TOXICITY

Carbamate compounds marked for their cholinesterase (ChE) inhibition a re widely used as therapeutics and as insecticides. Groups of closely related carbamate molecules provide an important tool in the understan ding of the domains responsible for binding these ligands to ChEs. Com parative inhibition profiles were derived for five N-methyl carbamates , mostly carbofuran derivatives, differing in length and branching of their hydrocarbonic chain towards human erythrocyte acetylcholinestera se (H.AChE), human serum butyrylcholinesterase (H.BChE) in its normal form or in a mutant form containing the point mutation ASP70-->Gly, an d Drosophila nervous system ChE. Carbofuran was more toxic to all thre e ChEs than any of the other derivatives, with IC50 values which diffe red by more than 1000-fold. Drosophila ChE appeared to be most sensiti ve to all of the examined carbamates, and H. AChE was consistently mor e sensitive than H. BChE. Morever, inhibition efficiency for H. BChE d ecreased more effectively than it did for H. AChE with increased lengt h and complexity of the side chain, indicating less flexible carbamate binding site in BChE as compared with AChE. The Asp70-->Gly mutation had no apparent effect on H. BChE inhibition by N-methyl carbamates, s uggesting that the ASP70 domain localized near the rim of the active s ite groove is not important in carbamate binding. Comparison of the ca rbamate IC50 values with published LD50 values demonstrated correlatio n between the in vivo toxicity and inhibition of BChE by carbamates, s uggesting a biological in addition to scavenging importance for BChE i n mammals. Pinpointing different domains characteristic of carbamate b inding in each member of the ChE family can thus shed light on the var iable toxicity of these inhibitors to insects and mammals, predict the toxicity of yet untested inhibitor molecules and help in designing no vel and improved ChE inhibitors.