PPIase that catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides and may therefore assist protein folding (By similarity). Involved in regulation of the mitochondrial permeability transition pore (mPTP) (PubMed:15800626, PubMed:15800627, PubMed:16103352, PubMed:18684715, PubMed:31489369). It is proposed that its association with the mPTP is masking a binding site for inhibiting inorganic phosphate (Pi) and promotes the open probability of the mPTP leading to apoptosis or necrosis; the requirement of the PPIase activity for this function is debated (PubMed:15800626, PubMed:15800627, PubMed:16103352, PubMed:18684715, PubMed:31489369). In cooperation with mitochondrial p53/TP53 is involved in activating oxidative stress-induced necrosis (PubMed:22726440). Involved in modulation of mitochondrial membrane F(1)F(0) ATP synthase activity and regulation of mitochondrial matrix adenine nucleotide levels (PubMed:19801635, PubMed:21281446). Has anti-apoptotic activity independently of mPTP and in cooperation with BCL2 inhibits cytochrome c-dependent apoptosis (By similarity). [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Binds cyclosporin A (CsA). Is displaced by CsA from the mPTP leading to a lower open probability of the mPTP. Associates with the mitochondrial membrane ATP synthase F(1)F(0) ATP synthase; the association is increased by inorganic phosphate (Pi) and decreased by cyclosporin A (CsA) (PubMed:19801635). Interacts with ATP5F1B; ATP5PD and ATP5PO (PubMed:21281446). Interacts with SLC25A3; the interaction is impaired by CsA (By similarity). Interacts with BCL2; the interaction is impaired by CsA. Interacts with TP53; the association implicates preferentially tetrameric TP53, is induced by oxidative stress and is impaired by CsA (PubMed:22726440). Interacts with C1QBP (PubMed:20950273). Interacts with MCUR1 (By similarity). Component of the mitochondrial permeability transition pore complex (mPTPC), at least composed of SPG7, VDAC1 and PPIF (By similarity). Interacts with SPG7 (By similarity). Acetylated at Lys-166; deacetylated at Lys-166 by SIRT3. Mice are developmentally normal and show no apparent anomalies (PubMed:15800626, PubMed:15800627, PubMed:16103352). Mitochondria do not undergo cyclosporin A-sensitive mitochondrial permeability transtition (PubMed:15800626, PubMed:15800627, PubMed:16103352). Cells show resistance to necrotic cell death induced by reactive oxygen species and Ca(2+) overload, and animals show a high level of resistance to ischaemia/reperfusion-induced cardiac injury (PubMed:15800626, PubMed:15800627, PubMed:16103352). Mice show a dramatic reduction in brain infarct size after acute middle cerebral artery occlusion and reperfusion (PubMed:15800626, PubMed:15800627, PubMed:16103352). Mice lacking Slc25a4/Ant1, Slc25a5/Ant2, Slc25a31/Ant4 and Ppif lack Ca(2+)-induced mitochondrial permeability transition pore (mPTP) formation (PubMed:31489369). Belongs to the cyclophilin-type PPIase family.