Hexokinaz

Hexokinaz is not a standardly recognized term in contemporary biochemistry. It may be a misspelling or variant of hexokinase, an enzyme that phosphorylates hexose sugars in the first step of glycolysis. In most biochemical literature, hexokinase refers to a family of isoenzymes rather than a single protein.

Hexokinase catalyzes the transfer of a terminal phosphate from ATP to the 6-hydroxyl group of a hexose, most commonly D-glucose, producing glucose-6-phosphate and ADP. The reaction traps glucose inside the cell and commits it to glycolysis, glycogen synthesis, or the pentose phosphate pathway, depending on cellular needs. Hexokinases generally have high affinity for glucose but low Km values, enabling efficient phosphorylation even at low glucose concentrations; glucokinase (HK4) has a higher Km and acts as a glucose sensor in liver and pancreatic beta cells.

Regulation and localization: Mammals express four hexokinase isozymes: HK1, HK2, HK3, and HK4 (glucokinase). HK1 and HK2 bind to the outer mitochondrial membrane via the voltage-dependent anion channel (VDAC), which couples glycolysis to respiration. HK4 is cytosolic in liver and regulated by glucokinase regulatory protein (GKRP) and blood glucose levels. In many cancers, HK2 is upregulated, supporting high glycolytic flux known as the Warburg effect.

Clinical and research relevance: Hexokinase activity is a point of intervention in metabolic disorders and cancer; several inhibitors have been studied to reduce glycolysis in tumors. Genetic or expression changes in hexokinase can affect glucose metabolism and energy production in tissues.