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 aci dic 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 a ctivity of NAALADase and the prostate enzyme PSM. METHODS. Using a NAAG hydrolytic radioenzymatic assay, we compared the phar macological and kinetic properties of the brain and prostate enzymes. RESULTS. Eight normal prostate tissues from different species exhibited NAA G hydrolyzing activity. Among 14 cancer cell lines examined, activity was o bserved in human LNCaP, PC-82, and rat Dunning G and AT-1 cells. Brain exhi bited membrane-localized activity exclusively, while the prostate enzyme ha d activity in both membrane and cytosolic fractions. The only observed phar macological difference was the sensitivity to their putative substrates, fo late polyglutamate and NAAG. Kinetically, the soluble form of the prostate enzyme had two catalytic sites, while the membrane-bound form exhibited sin gle site kinetics with a lower V-max than the brain enzyme, which may sugge st a less active hydrolase in the prostate. CONCLUSIONS. The brain enzyme NAALADase and the prostate enzyme PSM are rem arkably similar. The importance of the differences in substrate specificiti es and kinetic parameters remains to be elucidated. (C) 1999 Wiley-Liss, In c.