The “energized state” of mitochondria: Lifetime and ATP equivalence

Abstract

1. 1. Aequorin, a bioluminescent jellyfish protein, can measure the concentration of free Ca 2+ in a rapid, sensitive and specific manner, in biological systems. 2. 2. The movements of the nanomolar concentration of mitochondrial “endogenous” Ca 2+ have been studied, and found to be a reversible indicator of the energization of mitochondria. 3. 3. The comparison between the kinetics of cytochromes, changes on addition of respiratory inhibitors, and of the release of endogenous mitochondrial Ca 2+ has brought to the conclusion that the lifetime of the energized states is 7 ± 2 sec in rat-liver mitochondria at 25°. 4. 4. The energy content of the energized state was also determined, by comparing the kinetics of Ca 2+ efflux from mitochondria in the presence and absence of oligomycin and measuring the content of endogenous ATP. It was found to be 0.3 μmole ATP equivalents per g mitochondrial protein. 5. 5. The endogenous mitochondrial Ca 2+ has been found to be in a highly dynamic state. Therefore the proton movements observed on activation of respiration can be considered not primary, but associated with ion movements.