In vitro acetylcholinesterase inhibition by type A botulinum toxin.

Type A botulinum toxin was studied for its ability to inhibit the action of acetyl-cholinesterase. The chromogenic substrate, indophenyl acetate, was used for assay of enzyme activity. Inhibition of enzyme function was detected through use of both 6.6 x 10(-6) mg (20 ld(50)) and 6.6 x 10(-10) mg (2 x 10(-3)ld(50)) of type A botulinal toxin. Control assays were performed by use of both homologous antitoxin and heterologous antitoxins (types B and E). Enzyme inhibition was effectively prevented by use of homologous antitoxin only. The inhibition noted was specific and reproducible for given substrate, enzyme, and toxin concentrations.