GLUD1 and cancer: However, a direct and essential role of GDH in ammonium assimilation of cancer cells appears controversial because the GDH activities (Vmax) are lower in cancer mitochondria, and GDH shows very low affinity for ammonium, with apparent Michaelis–Menten constants (Km or K0.5) of 8 to 80 mM (27, 29–35).