The main enzymes involved in Gln metabolism found dysregulated in cancers are glutaminases (GLS and GLS2, each with at least two isoforms) and Glutamine Synthetase (GS), the only mammalian enzyme which operates the endoergonic reaction between Glu and free ammonium to produce Gln (Mates et al., 2019). Here, GLUL is linked to cancer.