Characterization of the enzymatic activity of PSM: comparison with brain NAALADase.
BACKGROUND
The prostate cancer marker prostate-specific membrane antigen (PSM) is highly homologous to the brain enzyme N-acetylated alpha-linked acidic dipeptidase (NAALADase). NAALADase is known to cleave terminal carboxy glutamates from both the neuronal peptide N-acetylaspartylglutamate (NAAG) and folate polyglutamate. In this report, we compare the NAAG hydrolyzing activity of NAALADase and the prostate enzyme PSM.


METHODS
Using a NAAG hydrolytic radioenzymatic assay, we compared the pharmacological and kinetic properties of the brain and prostate enzymes.


RESULTS
Eight normal prostate tissues from different species exhibited NAAG hydrolyzing activity. Among 14 cancer cell lines examined, activity was observed in human LNCaP, PC-82, and rat Dunning G and AT-1 cells. Brain exhibited membrane-localized activity exclusively, while the prostate enzyme had activity in both membrane and cytosolic fractions. The only observed pharmacological difference was the sensitivity to their putative substrates, folate polyglutamate and NAAG. Kinetically, the soluble form of the prostate enzyme had two catalytic sites, while the membrane-bound form exhibited single site kinetics with a lower Vmax than the brain enzyme, which may suggest a less active hydrolase in the prostate.


CONCLUSIONS
The brain enzyme NAALADase and the prostate enzyme PSM are remarkably similar. The importance of the differences in substrate specificities and kinetic parameters remains to be elucidated.
Tiffany
C W
CW
Guilford Pharmaceuticals, Inc., Baltimore, Maryland 21224, USA.
Lapidus
R G
RG
Merion
A
A
Calvin
D C
DC
Slusher
B S
BS
D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D000954:Antigens, Surface; D001921:Brain / Q000201:enzymology*; D002268:Carboxypeptidases / Q000378:metabolism*; D043425:Glutamate Carboxypeptidase II; D006801:Humans; D007700:Kinetics; D008297:Male; D011471:Prostatic Neoplasms / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014407:Tumor Cells, Cultured
D000951:Antigens, Neoplasm; D000954:Antigens, Surface; D002268:Carboxypeptidases; C473848:FOLH1 protein, human; D043425:Glutamate Carboxypeptidase II