ADP:ATP antiporter that mediates import of ADP into themitochondrial matrix for ATP synthesis, and export of ATP out to fuelthe cell. Cycles between the cytoplasmic-open state (c-state) and the matrix-open state (m-state) : operates by the alternatingaccess mechanism with a single substrate-binding site intermittentlyexposed to either the cytosolic (c-state) or matrix (m-state) side ofthe inner mitochondrial membrane. Specifically requiredduring spermatogenesis, probably to mediate ADP:ATP exchange inspermatocytes. Large ATP supplies from mitochondriamay be critical for normal progression of spermatogenesis during earlystages of meiotic prophase I, including DNA double-strand break repairand chromosomal synapsis. In addition to its ADP:ATPantiporter activity, also involved in mitochondrial uncoupling andmitochondrial permeability transition pore (mPTP) activity. Plays a role in mitochondrial uncoupling by acting as aproton transporter: proton transport uncouples the proton flows via theelectron transport chain and ATP synthase to reduce the efficiency ofATP production and cause mitochondrial thermogenesis. Proton transporter activity is inhibited by ADP:ATP antiporteractivity, suggesting that SLC25A31/ANT4 acts as a master regulator ofmitochondrial energy output by maintaining a delicate balance betweenATP production (ADP:ATP antiporter activity) and thermogenesis (protontransporter activity). Proton transporter activityrequires free fatty acids as cofactor, but does not transport it. Also plays a key role in mPTP opening, a non-specific porethat enables free passage of the mitochondrial membranes to solutes ofup to 1. 5 kDa, and which contributes to cell death. Itis however unclear if SLC25A31/ANT4 constitutes a pore-formingcomponent of mPTP or regulates it.

MHREPAKKKAEKRLFDASSFGKDLLAGGVAAAVSKTAVAPIERVKLLLQVQASSKQISPEARYKGMVDCLVRIPREQGFFSFWRGNLANVIRYFPTQALNFAFKDKYKQLFMSGVNKEKQFWRWFLANLASGGAAGATSLCVVYPLDFARTRLGVDIGKGPEERQFKGLGDCIMKIAKSDGIAGLYQGFGVSVQGIIVYRASYFGAYDTVKGLLPKPKKTPFLVSFFIAQVVTTCSGILSYPFDTVRRRMMMQSGEAKRQYKGTLDCFVKIYQHEGISSFFRGAFSNVLRGTGGALVLVLYDKIKEFFHIDIGGR