Glutamate carboxypeptidase II is not an amyloid peptide-degrading enzyme.

ABSTRACT

Glutamate carboxypeptidase II (GCPII) is an exopeptidase that catalyzes the hydrolysis of N-acetylated aspartate-glutamate (NAAG) to N-acetyl aspartate (NAA) and glutamate. Consequently, GCPII inhibition has been of interest for the treatment of central and peripheral nervous system diseases associated with excess glutamate. Recently, it was reported that GCPII can also serve as an endopeptidase cleaving amyloid ß (Aß) peptides and that its inhibition could increase the risk of Alzheimer's disease by increasing brain Aß levels. This study aimed to corroborate and extend these new findings. We incubated Aß peptides (20 µM) with human recombinant GCPII (300 ng/ml) and monitored the appearance of degradation products by mass spectrometry. Aß peptides remained intact after 18 h incubation with GCPII. Under the same experimental conditions, Aß1-40 (20 µM) was incubated with neprilysin (300 ng/ml), an endopeptidase known to hydrolyze Aß1-40 and the expected cleavage products were observed. GCPII was confirmed active by catalyzing the complete hydrolysis of NAAG (100 µM). We also studied the hydrolysis of [(3)H]-NAAG (30 nM) catalyzed by GCPII (40 pM) in the presence of Aß peptides (picomolar to micromolar range). The addition of Aß peptides did not alter [(3)H]-NAAG hydrolysis. We conclude that GCPII is not an amyloid peptide-degrading enzyme.