ASPG and neoplasm: Such aspartate depletion strategy may be effective particularly for tumor cells in vivo, since aspartate availability is quite limited in the microenvironment because of the low permeability of the cell membrane to it (19, 20), its low blood level (21, 32), and the fact that the asparaginase activity necessary to convert asparagine to aspartate is absent in most mammals (33–35).