Fig. 2. Energy export from mitochondria matrix and intracristal space. Restricted diffusion of nucleotides from the narrow intracristal space to the external compartment could be overcome by an enzymatic system and/or by high-throughput contact sites traversing the inner (im) and outer (om) membranes. In some circumstances, contact sites could provide direct access to ATP in the matrix compartment, while intracristal space could be used for proton confinement leading to efficient ATP synthesis. E, E₁, E₂, near-equilibrium phosphotransfer enzymes; ANT, adenine nucleotide translocator.