The invention relates to a methionine gamma lyase-2-aminobutyrate deaminase (MEGL-2ABD) enzyme and provides an isotopic assay for quantitatively measuring activity of the enzyme. The MEGL-2ABD is a therapeutic target for cancer, particularly in cancer stem cells and their lineages. The invention additionally provides a protein, MEGL-2ABD (SEQ ID NO:2), compositions/formulations containing this protein, and methods/assays for using this protein in therapeutic applications allowing progress toward prevention, diagnosis, treatment, and cure of cancer.
