PARL regulates mitochondrial remodelling and apoptosis through regulated substrate proteolysis. It is required for the control of apoptosis during postnatal growth and is essential for processing an antiapoptotic form of OPA1, which prevents release of mitochondrial cytochrome c in response to intrinsic apoptotic signals. It also promotes processing of DIABLO/SMAC, which is required for DIABLO apoptotic activity.

PARL also acts as a sensor of mitochondrial health. It is required for maturation of PINK1 into its 52 kDa mature form after cleavage by mitochondrial-processing peptidase. When mitochondrial membrane potential is lost, PARL dissociates from PINK1 and associates with the phosphatase PGAM5, promoting PGAM5 cleavage in damaged mitochondria. This gives differential cleavage of PINK1 and PGAM5 according to mitochondrial status. Further substrates include CLPB, where removal of an autoinhibitory N-terminal peptide gives a form with higher protein disaggregase activity, STARD7, whose processing regulates its location between mitochondria and cytosol, and TTC19. PARL also promotes changes in mitochondrial morphology that are regulated by phosphorylation of its P-beta domain.

The PARL gene encodes a member of the rhomboid family and belongs to the peptidase S54 family. Proteolytic processing of the protein releases a small peptide, P-beta, which may transit to the nucleus, consistent with the nuclear location listed for PARL. Mutations in the gene may be associated with Parkinson's disease. Mouse and rat orthologs are both named Parl.