An ATPase is an enzyme that catalyzes the decomposition of ATP into ADP plus an inorganic phosphateion. This dephosphorylation is widely used in all known forms of life as a mechanism for driving energetically unfavourable reactions; as such, ATPases are rarely dedicated solely to dephosphorylating ATP, but rather couple this reaction to some other reaction and use the ATP dephosphorylation as a source of energy.
