PROTEOLYSIS AT THE SECRETASE AND AMYLOIDOGENIC CLEAVAGE SITES OF THE BETA-AMYLOID PRECURSOR PROTEIN BY ACETYLCHOLINESTERASE AND BUTYRYLCHOLINESTERASE USING MODEL PEPTIDE-SUBSTRATES

1. It was recently proposed that acetylcholinesterase (AChE), in addit ion to its esteratic activity, has proteolytic activity such that it m ay cleave the beta-amyloid precursor (beta-APP) within the beta-amyloi d sequence. The purpose of this paper was to examine further whether A ChE or butyrylcholinesterase (BuChE) had associated proteinase activit y, that was involved in the metabolism of beta-APP. 2. The ability of various preparations of AChE and BuChE to hydrolyze two synthetic frag ments of beta-APP695 as model substrates containing the normal and abe rrant cleavage sites was studied. 3. Digestion of these synthetic subs trates with commercial preparations of Electrophorus electricus AChE i ndicated the presence of a trypsin-like proteolytic activity cleaving each peptide at the carboxy-terminal side of an internal lysine residu e. 4. Purification of the trypsin-like proteinase activity by aminoben zamidine affinity chromatography yielded a preparation that was devoid of AChE activity but retained all of the proteinase activity. 5. Amin o-terminal sequence analysis of this preparation showed that the first 13 amino acid residues were identical to beta-pancreatic trypsin. 6. These data indicate that the proteinase activity found in these commer cial preparations of AChE is due to contamination with trypsin.