Computer graphics representation of the ATP- binding domain (reaction site) of phosphoglycerate kinase, a glycolytic enzyme (catalyst). In glycolysis, glucose is converted to pyruvate with the production of ATP: in other words, a catabolic reaction provides metabolic energy (as ATP) at the expense of the degradation of food molecules (glucose). Kinase enzymes catalyse the transfer of phosphoryl groups from one substrate (usually ATP) to another. In this view of part of the horse phosphoglycerate kinase molecule, the alpha carbon backbone appears as a blue ribbon, with ATP bound with a green Van der Waal's surface. Phosphate oxygens of ATP are highlighted by red sticks, with the adenine ring in blue and white.