a glycolytic enzyme that catalyzes the reaction ATP + D-hexose = ADP + D-hexose 6-phosphate. The first and rate-limiting step in glycosis, a pathway that produces energy in the form of ATP from glucose. An allosteric enzyme inhibited by its product glucose-6-phosphate (Glc-6-P). HK-2 and its mitochondrial receptor (VDAC) play the most pivotal and direct roles in the ""Warburg effect"". Acts as a ""glucose sensor"" by trapping glucose inside the cell by catalyzing its phosphorylation to produce Glc-6-P. In vertebrates there are four major glucose-phosphorylating isoenzymes, designated hexokinase I, II, III and IV (glucokinase). Four human isoforms are produced by alternative splicing and alternative initiation. Isoform HK1 is markedly elevated in rapidly growing tumor cells exhibiting high glucose catabolic rates. HK1 is present in most tissues but is especially prominent in brain and kidney. Isoform HK1-SC is is an integral membrane protein detected in round spermatids, condensing spermatids and mature sperm where it is found in the head membranes, mitochondria of the midpiece and the fibrous sheath of the flagellum. Isoform HK1-SA is first expressed during meiosis and continues to be present in postmeiotic germ cells while isoform HK1-SB is present only in postmeiotic germ cells. Note: This description may include information from UniProtKB.
Protein type: Carbohydrate Metabolism - amino sugar and nucleotide sugar; Carbohydrate Metabolism - fructose and mannose; Carbohydrate Metabolism - galactose; Carbohydrate Metabolism - glycolysis and gluconeogenesis; Carbohydrate Metabolism - starch and sucrose; EC 18.104.22.168; Kinase, other; Mitochondrial