NAAG biosynthesis has been studied for well over a decade, and yet to date, no NAAG biosynthetic enzyme has been isolated and characterized. The presence of a "NAAG synthetase" enzyme has been demonstrated indirectly in tissue culture and tissue explants,27 but no data on the incorporation of radiolabeled precursors into NAAG have been reported in tissue homogenates. Protein synthesis inhibitors have no effect on incorporation of radiolabeled precursors into NAAG,28 indicating that NAAG is not synthesized ribosomally as a portion of a protein, and then later cleaved to generate the active molecule. Because the ability of neurons to synthesize NAAG is lost when tissue explants are homogenized, it seems clear that "NAAG synthase" is either sequestered in a membrane compartment where optimal conditions are maintained for enzyme activity, or that the mixing of extracellular and intracellular constituents brings the enzyme in contact with salts, proteases or inhibitors that render it inactive.
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