hexokinase

The first enzyme of glycolysis, converting intracellular glucose to Glucose-6-Phosphate, using the gamma phosphate of ATP. The enzyme in bacteria and yeast contains a single domain (50 kDa) and is located in the cytosol. In higher organisms, the enzyme is composed of two distinct domains similar in structure to the former, but differing in function:

• C-terminal domain: Contains the catalytic activity of mammalian hexokinase.
• N-terminal domain: Devoid of catalytic activity in the mammalian types I (brain) and III, but active in type II (muscle). It contributes regulatory properties to the holoenzyme, such as sensitivity to product inhibition by G6P. This domain of mammalian hexokinase in brain and muscle (HK-I, HK-III) confers to the enzyme the ability to associate with porin on the outer membrane of various mitochondria. This specific localization, enabling a tight coupling between glycolysis and oxidative phosphorylation, is sensitive to G6P.

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last update, Dec 1999 - Claude Aflalo - suggestions are welcome...