Interdependence between mitochondrial matrix volume and the extramitochondrial ratio of [ATP]/[ADP] [inorganic phosphate].

ATP or combinations of ATP with EDTA and EGTA can act as chelators to support succinate-driven, phosphate-requiring expansion of mitochondrial inner membrane-matrices. Contraction of these swollen mitochondria can be induced with antimycin, MgCl₂ and ADP. The magnitude of ADP-induced contraction of mitochondria, swollen in the presence of ATP, is dependent on ADP] and may be altered by the extramitochondrial concentrations of both P_i and ATP. In fact, the extent of contraction (+ΔA₅₂₀) is a linear function of the thermodynamic parameter, ?ΔGp (free energy of hydrolysis of ATP), provided excessive concentrations of reactants are not present and the extents of matrix swelling are similar ($\text{e.g.}\text{ΔA}{}_{520}$ is about 0.250) before starting contraction with ADP.