IDH1 and glioblastoma: Of note, many metabolites are substrates for more than 1 enzyme; thus, single comparisons of enzymatic activity and metabolite levels do not necessarily correlate — e.g., in the case of glutamate where we identified in the IDH1-WT glioblastoma group a total of 3 upregulated (OPLAH, EARS2, GOT1) and 2 downregulated (GLUD1, GCLC) enzymes (Figure 4C).