Adenosine triphosphatase, an enzyme that hydrolyzes (clips the bond between two phosphates in) ATP to yield ADP, phosphate, and energy. The reaction is usually coupled to an energy-requiring process. ATP is hydrolyzed in the act of shivering and the energy produced is converted into heat to increase body temperature. This type of heat production involves what is known as a futile cycle because the energy is converted to (and wasted as) heat rather than used in motion, etc.
A group of enzymes that catalyze the removal or addition of a single phosphate group to the high- energy compound containing adenine. In the direction of cleavage ATP ADP Pi; in the reverse, ADP + Pi -> ATP.