GLUL and hepatocellular carcinoma: A similar result was evident for HCC; LC-MS/MS analysis on serum samples of 30 healthy subjects and 30 patients revealed a significant decrease in D-Glu and D-Gln (1.9- and 1.6-fold lower, respectively, see Table 1) for HCC compared to controls, probably due to the over-expression of glutamine synthetase, an enzyme that is not enantiospecific and, thus, catalyzes the synthesis of glutamine from both L-Glu and D-Glu [64].