BIOCHEMICAL-CHARACTERIZATION OF AMINOSTIGMINE, A NOVEL ANTICHOLINESTERASE DRUG

In vitro biochemical characteristics of aminostigmine were compared wi th those of other carbamates that inhibit cholinesterases. The bimolec ular inhibition rate constants for acetyl-, butyryl-, and propionylcho linesterases were (8.0-14.0). 10(5), (3.8-7.7). 10(5), and 11.0-10(5) M(-1). min(-1), respectively. The inhibitory activity of aminostigmine equals that of proserine, is less than that of physostigmine, and exc eeds that of pyridostigmine. Decarbamylation rate constants of aminost igmine-inhibited acetylcholinesterase were (1.1-1.6). 10(-2), (2.5-2.8 ). 10(-2), and 0.025 . 10(-2) min(-1) when assayed by dilution, additi on of acetylcholine excess, and dialysis, respectively, In general, am inostigmine is a slow and reversible inhibitor. Aminostigmine-carbamyl ated enzyme was not reactivated by cholinesterase reactivators such as TMB-4 and HI-6. At (4-6). 10(-7) M aminostigmine blocks irreversible suppression of cholinesterase by some organophosphorus inhibitors by 5 0%; these concentrations of OPI inhibit its enzymatic activity by 85-9 0%.