PHGDH and cancer: In terms of glutamine metabolism, a study on pancreatic ductal adenocarcinoma revealed that the cancer cells are highly dependent on a specific glutamine catabolic pathway, and malate dehydrogenase (MDH1) is a key enzyme in this pathway.128 Zhu et al. found that Ser189 was the glycosylation site of MDH1, and its O-GlcNAc glycosylation could promote Gln catabolism.