Comparison of aminopeptidase, dipeptidyl aminopeptidase and tripeptidyl aminopeptidase activities in brain tissue from normal and Alzheimer's disease cases.

Recent evidence has suggested that Alzheimer's disease may result from an underlying defect of protein catabolism. In an attempt to identify such a defect, we have undertaken the systematic identification and characterization of the proteolytic enzymes responsible in human brain for oligopeptide breakdown via hydrolysis of NH2-terminal residues--the aminopeptidases, dipeptidyl aminopeptidases and tripeptidyl aminopeptidases. The activities of these enzymes were determined following anion exchange chromatographic fractionation of cortical soluble extracts, to prevent interference in the respective assay procedures by the major cortical aminopeptidase. Corresponding enzyme types showed similar levels of activity in soluble extracts of frontal cortex from normal and Alzheimer's disease cases. These data suggest that the characteristic neurodegeneration associated with Alzheimer's disease does not result from altered aminopeptidase, dipeptidyl aminopeptidase or tripeptidyl aminopeptidase activity in cortical tissues of patients with this disorder.