Cathepsin D from Alzheimer's-diseased and normal brains.
An acid protease activity from human brain was found to cleave a fluorogenic peptide substrate encompassing the amino terminus of Alzheimer's amyloid-beta peptide (A beta). The protease was isolated and determined to be cathepsin D based on chromatographic, immunological, and enzymatic data. Analysis of the cleavage sites indicated that cathepsin D hydrolyzed the methionine--aspartate bond generating the in vivo amino terminus of A beta. These data suggested that cathepsin D could be involved in amyloidogenic processing of the amyloid precursor protein. Consequently, cathepsin D from both Alzheimer's-diseased and control brains was compared to determine whether there were any differences which could account for an increase in A beta production in Alzheimer's disease. No differences were detected in isoform composition or tissue content of cathepsin D as measured by 2-D IEF-SDS-PAGE. Enzymological characterization of brain cathepsin D demonstrated that it could undergo a previously undescribed pH-dependent reversible activation. However, that activation appeared identical for both AD and normal brain enzymes. These data demonstrate that concentration, isoform distribution, and several enzymological characteristics of cathepsin D are not distinguishable between AD and normal brain. The pH dependence of cathepsin D activity suggests, however, that its intracellular localization may be important in considering the potential role of cathepsin D in Alzheimer's disease.
Kohnken
R E
RE
Diagnostic Division, Abbott Laboratories, Abbott Park, Illinois 60064, USA.
Ladror
U S
US
Wang
G T
GT
Holzman
T F
TF
Miller
B E
BE
Krafft
G A
GA
D000368:Aged; D000544:Alzheimer Disease / Q000378:metabolism*; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D002402:Cathepsin D / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D007536:Isomerism; D008875:Middle Aged; D012016:Reference Values
D016282:Aspartic Acid Endopeptidases; D002402:Cathepsin D