Catalyzes the phosphorylation of hexose, such as D-glucose and D-fructose, to hexose 6-phosphate (D-glucose 6-phosphate and D-fructose 6-phosphate, respectively). Mediates the initial step of glycolysis by catalyzing phosphorylation of D-glucose to D-glucose 6-phosphate. Plays a key role in maintaining the integrity of the outer mitochondrial membrane by preventing the release of apoptogenic molecules from the intermembrane space and subsequent apoptosis. ATP + D-hexose = ADP + D-hexose 6-phosphate + H(+) ATP + D-fructose = ADP + D-fructose 6-phosphate + H(+) ATP + D-glucose = ADP + D-glucose 6-phosphate + H(+) Hexokinase activity is specifically inhibited by 2,6-disubstituted glucosamines. Carbohydrate metabolism; hexose metabolism. Carbohydrate degradation; glycolysis; D-glyceraldehyde 3-phosphate and glycerone phosphate from D-glucose: step 1/4. Monomer (By similarity). Interacts with TIGAR; the interaction increases hexokinase activity in a hypoxia- and HIF1A-dependent manner (By similarity). The mitochondrial-binding peptide (MBP) region promotes association with the mitochondrial outer membrane. The interaction with the mitochondrial outer membrane via the mitochondrial-binding peptide (MBP) region promotes higher stability of the protein. Release from the mitochondrial outer membrane into the cytosol induces permeability transition pore (PTP) opening and apoptosis. The N- and C-terminal halves of the protein contain a hexokinase domain. In contrast to hexokinase-1 and -3 (HK1 and HK3, respectively), both hexokinase domains display catalytic activity. The region connecting the two hexokinase domains is required for the catalytic activity of the N-terminal hexokinase domain. The N-terminal half regulates stability of the whole enzyme. Belongs to the hexokinase family.