Substrate preferences of wild and a mutant house fly acetylcholinesterase and a comparison with the bovine erythrocyte enzyme.

Comparisons were made of purified acetylcholinesterase from the heads of wild type house flies with a mutant form (which bound organophosphates and carbamates less tightly). Using 12 substrates and 6 quaternary inhibitors, the only substantial difference was that the Km for butyrylcholine was 25 times greater for the mutant enzyme, suggesting that butyrylcholine and the organophosphates and carbamates shared a common binding site. The pure enzyme from the wild type house fly was also compared with bovine erythrocyte acetylcholinesterase. The major difference was again with butyrylcholine as substrate: the ability to acylate or deacylate was 30 times greater in the fly enzyme (the Km values differed by a factor of 4).