Fig. 2.

Sources, biosynthesis, and effects of glutamine. Tumor cells have the ability to take up glutamine from extracellular fluids and synthesize de novo glutamine intracellularly (not shown in the figure). Tumor cells can also use two distinct layers of membrane structures to encapsulate intracellular proteins and organelles, which are then fused with the lysosomes and digested to release glutamine. In addition, some tumor cells can also deliver proteins or cells to the lysosomes for digestion and subsequently release glutamine through the processes of macropinocytosis, entosis and phagocytosis (1). The glutamine taken up by the tumor cells can be effectively used to synthesize fatty acids, ATP, proteins, amino acids, nucleotides and glutathione (2), which will ultimately be used for the survival, growth and reproduction of the tumor cells (3)