ADP delivery from adenylate kinase in the mitochondrial intermembrane space to oxidative phosphorylation increases in the presence of macromolecules

Macromolecules were added to isolated rat liver mitochondria to mimic cytosolic macromolecules and tested for their effects on the ADP delivery from adenylate kinase in the intermembrane space to oxidative phosphorylation. In the presence of 10% (w/v) dextran M20 or bovine serum albumin, approximately 60% of the maximal ADP flux from adenylate kinase to oxidative phosphorylation was not accessible to an extramitochondrial ADP scavenger. In the absence of macromolecules this was 34%. ADP determinations from incubations with macromolecules demonstrated the existence of flux-dependent ADP concentration gradients across the outer membrane which can be as high as 12 µM.