Computer graphics image of an ATP molecule bound to phosphoglycerate kinase, a glycolytic enzyme. 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 example of horse kinase, the alpha carbon backbone appears as a yellow ribbon, with ATP highlighted in green. Bonding of oxygen, carbon & nitrogen atoms of ATP appears in red, white & blue respectively. Bonding" refers to the Van der Waal's surface, a weak bond binding the reactant to substrate."