Adenosine triphosphate (ATP) is a nucleotid and functions as the major carrier of chemical energy in the cells. As it transfers its energy to other molecules, it loses its terminal phosphate group and becomes adenosine diphosphate (ADP).

Magnesium Green (MgG), an extrinsic fluorophore, can be applied for measurement of mitochondrial ATP production with mitochondrial preparations. This dye fluoresces when bound to Mg²⁺. The technique to measure mitochondrial ATP production is based on the fact that Mg²⁺ presents different dissociation constants for ADP and ATP, and the adenine nucleotide translocase (ANT) exchanges ATP for ADP.