Shoest acting anticholinesterase is ?

Ans. is 'a' i.e., Edrophonium Edrophonium is the shoest acting anti-ChE. When carbamates (other than edrophonium) and organophophates react with cholinesterase, they form covalent bond at esteratic site, which is considerably resistant to hydrolysis. In contrast, edrophonium binds electrostatically and by hydrogen bonds at anionic site (not at esteratic site) of cholinesterase. The enzyme inhibitor complex does not involve a covalent bond and is correspondingly sho lived (2-10 minutes). So edrophonium is also called as noncovalent inhibitor.