POTENTIAL BETA-PP-PROCESSING PROTEINASE ACTIVITIES FROM ALZHEIMERS AND CONTROL BRAIN-TISSUES

Fluorogenic peptide substrates designed to encompass the reported alph a-secretory and amyloidogenic cleavage sites of the amyloid-beta precu rsor protein (beta PP) were used to analyze proteinase activities in b rain extracts from control patients and those with Alzheimer's disease (AD). Activity against the secretory substrate at pH 7.5 in control a nd AD brains produced a major endopeptidase cleavage at the Lys687-Leu 688 bond (beta PP770 numbering), consistent with the beta PP secretase cleavage. Activity in control brains against the amyloidogenic substr ate at pH 7.5 produced one cleavage at the Ala673-Glu674 bond, two res idues C-terminal to the amyloidogenic Met-Asp site. However, in three of four AD brains, the major cleavage was at the Asp-Ala bond, one res idue from the amyloidogenic site. Both endopeptidase and carboxypeptid ase activities in AD brains were lower than in control brains. Protein ase activities against the secretory substrate had a major optimum at pH 3.0-4.0 and another at pH 6.0-7.5. Proteinase activities against th e amyloidogenic substrate had a major optimum at or below pH 3.0 and a nother at pH 6.0. Using both substrates, activities at low pH were hig her in AD brains than in controls, while at pH above 6.5, activities i n control brains were higher than in AD. These results indicate that t he levels of proteolytic enzymes in AD brains are altered relative to controls.