GGT1 and glioblastoma: As shown in Fig. 4A, glioblastoma tumor tissues showed higher expression of the GGT isoforms GGT1 and GGT2 compared to contralateral normal-appearing or tumor-free healthy brain tissues (3.06 ± 0.31 a.u., 1.00 ± 0.08 a.u. and 1.14 ± 0.14 a.u. for tumor, contralateral normal-appearing brain and healthy brain respectively; p = 0.03 tumor versus contralateral normal-appearing brain and p = 0.02 tumor versus healthy brain; Fig. 4A,B, Supplementary Fig. 2).