Has both folate hydrolase and N-acetylated-alpha-linked-acidic dipeptidase (NAALADase) activity. Has a preference for tri-alpha-glutamate peptides (By similarity). In the intestine, required for the uptake of folate. In the brain, modulates excitatory neurotransmission through the hydrolysis of the neuropeptide, N-aceylaspartylglutamate (NAAG), thereby releasing glutamate. Also exhibits a dipeptidyl-peptidase IV type activity. In vitro, cleaves Gly-Pro-AMC. Release of an unsubstituted, C-terminal glutamyl residue, typically from Ac-Asp-Glu or folylpoly-gamma-glutamates. Binds 2 Zn(2+) ions per subunit. Required for NAALADase activity. The NAALADase activity is inhibited by beta-NAAG, quisqualic acid and 2-(phosphonomethyl)glutaric acid (PMG). Homodimer. Experimental confirmation may be lacking for some isoforms. Widely expressed throughout brain regions with highest levels in the hippocampus, dentate gyrus, priform cortex, choroid plexus of ventricles, pineal gland, anterior lobe of the pituitary gland and supraoptic nucleus. High levels also found in the cerebral cortex, substantia nigra, pontine nucleus and the granule cell layer of cerebellum. Highly expressed in astrocytes and non-myelinating Schwann cells. Also expressed in kidney, localizing to the proximal brush border of the renal tube. The NAALADase activity is found in the central region, the dipeptidyl peptidase IV type activity in the C-terminal. Probably inactive. Belongs to the peptidase M28 family. M28B subfamily.