[The peptidase site of butyrylcholinesterase is distinct from the esterase site]

Highly purified human plasma butyrylcholinesterase was inhibited by reversible inhibitors of esterase activity and modified by active-site-directed irreversible inhibitors of esterases and proteases. Peptidase and esterase activities of inhibited enzyme were simultaneously essayed from rates of hydrolysis of substance P (first cleavage) and butyrylthiocholine respectively. Inhibition parameters values and rates of inactivation of the two activities provide evidence that the peptidasic site is distinct from the esteratic site.