 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.Due to low glutamate dehydrogenase and glutamate pyruvate transaminase activities, in tumor cells the conversion of glutamate to alpha-ketoglutarate mainly takes place via glutamate oxaloacetate transaminase.