Hexokinase is the first enzyme in the glycolytic pathway, catalyzing the transfer of a phosphoryl group from ATP to glucose to form glucose-6-phosphate and ADP. In mammals, four distinct enzymes-types 1 to 4 hexokinases-have been identified. The enzyme is found in most cells, but there is tissue specificity for the particular type of hexokinase. Hexokinase1 is found in the adipose tissue and liver and encodes a ubiquitous form of hexokinase which localizes to the outer membrane of mitochondria. A deficiency in hexokinase 1 is implicated in the rare hereditary autosomal recessive disease known as nonspherocytic haemolytic anaemia.
In yeast there are three glucose-phosphorylating isoenzymes, designated hexokinase I, II and glucokinase. Present with 40800 molecules/cell in log phase SD medium.