Hexokinase

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A hexokinase is an enzyme that phosphorylates a six-carbon sugar, a hexose, to a hexose phosphate. In most tissues and organisms, glucose is the most important substrate of hexokinases, and glucose-6-phosphate the most important[citation needed] product.

Contents

Variation across species

Genes that encode hexokinase have been discovered in each domain of life, ranging from bacteria, yeast, and plants to humans and other vertebrates. They are categorized as actin fold proteins, sharing a common ATP binding site core surrounded by more variable sequences that determine substrate affinities and other properties. Several hexokinase isoforms or isozymes providing different functions can occur in a single species. Hexokinase should not be confused with the liver's glucokinase. While hexokinase is capable of phosphorylating several hexoses, glucokinase acts with a 50-fold lower substrate affinity, and its only substrate is glucose.

Reaction

The intracellular reactions mediated by hexokinases can be typified as:

where hexose-CH2OH represents any of several hexoses (like glucose) that contain an accessible -CH2OH moiety. Action of Hexokinase on Glucose

Consequences of hexose phosphorylation

Phosphorylation of a hexose such as glucose often limits it to a number of intracellular metabolic processes, such as glycolysis or glycogen synthesis. Phosphorylation makes hexose unable to move or be transported out of the cell.

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