Glutaminolysis takes place in all proliferating cells, such as lymphocytes, thymocytes, colonocytes, adipocytes and especially in tumor cells. Glutaminolysis has been targeted for therapeutic purposes. In tumor cells the citric acid cycle is truncated due to an inhibition of the enzyme aconitase (EC 4.2.1.3) by high concentrations of reactive oxygen species (ROS)  Aconitase catalyzes the conversion of citrate to isocitrate. 
On the other hand, tumor cells over express phosphate dependent glutaminase and NAD(P)-dependent malate decarboxylase, which in combination with the remaining reaction steps of the citric acid cycle from α-ketoglutarate to citrate impart the possibility of a new energy producing pathway, the degradation of the amino acid glutamine to glutamate, aspartate, pyruvate CO, lactate and citrate.
Besides glycolysis in tumor cells glutaminolysis is another main pillar for energy production. High extracellular glutamine concentrations stimulate tumor growth and are essential for cell transformation. On the other hand, a reduction of glutamine correlates with phenotypical and functional differentiation of the cells.