HK2 and central nervous system cancer: The rate-limiting, irreversible and glycolysis-related enzymes hexokinase (HK2 and HK3) and pyruvate kinase (PKM2), but not HK1 or the pyruvate kinase isoform PKLR, were also expressed at lower levels in IDH1MUT glioma compared with IDH1WT glioma (Figure 1).