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) (By similarity). Mediates the initial step of glycolysis by catalyzing phosphorylation of D-glucose to D-glucose 6-phosphate (By similarity). 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 (PubMed:18350175). 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. Predominantly expressed in skeletal muscle, heart and adipose tissues. 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. Embryonic lethality around E7.5 stage probably caused by the absence of hexokinase activity. Belongs to the hexokinase family.