ATP is a nucleotide, which stores the energy liberated during conversion of carbohydrates to carbon dioxide and water in metabolism. The energy is stored by means of the phosphate ester linkages (many enzyme processes are coupled with phosphate ester hydrolysis). Hydrolysis of the terminal phosphate linkage of ATP is accompanied by an internal energy decrease for two main reasons. ATP is highly negatively charged with four negative charges present on the phosphate groups (two on the terminal phosphate and one each on the two others). Hydrolysis enables the separation of these negative charges from each other. Secondly, there is greater resonance stabilization in ADP than in ATP.