Shoest acting anticholinesterase is -

Ans. is 'a' i.e., Edrophonium o Edrophonium is the shoest acting anti-ChE. o Why is it so, lets see : o When carbamates (other than edrophonium) and organophophates react with cholinesterase, they form covalent bond at esteratic site, which is considerably resistant to hydrolysis. o 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). o So edrophonium is also called as noncovalent inhibitor.