Hexokinase is the first enzyme to change glucose during the energy investment phase of glycolysis. The function of hexokinase is to phosphorylate glucose and in the process reduce ATP into ADP. This replacement of a hydrogen with a phosphate makes glucose remain in the cell because the negative charge of phosphate excludes the possibilty of traversing the plasma membrane. Glucose also becomes more reactive due to this change.

Since hexokinase is involved in a necessary function for cell survival, it is found in many different types of organisms. The links below show five different organisms and the sequence of hexokinase in each case. Click on images or words.