The enkephalins are amongst the peptides hydrolyzed by purified acetylcholinesterase.

We have shown that purified acetylcholinesterase has the ability to hydrolyze a number of peptides including the physiologically occurring enkephalins. The enkephalins lost both the amino- and carboxyl-terminal amino acids, but several other peptides were not degraded. The enzyme was purified using an affinity chromatographic matrix that recognised one component of the active centre that is specific to cholinesterases, the anionic-binding site. The acetylcholinesterase was extracted from four tissues of diverse origin to minimise the risk of co-purifying a peptidase. The enzyme was essentially homogeneous on polyacrylamide gels, and there was only one protein that bound diisopropylfluorophosphate in the samples. The peptidase activity was not affected by the aminopeptidase inhibitor puromycin, but it was inhibited by acetylcholine at concentrations that also reduced the esterase activity. It was concluded that acetylcholinesterase also has the capacity for a novel type of hydrolysis of peptide bonds. The ability of acetylcholinesterase to hydrolyse naturally occurring compounds of different chemical nature, like esters and peptides, may help explain the long-standing puzzle of why the enzyme is more widely distributed than acetylcholine, once thought to be its sole natural substrate. The localization of the enzyme probably more accurately reflects the distribution of all its substrates, although their identity remains to be determined.