Required for the control of apoptosis during postnatal growth (PubMed:16839884). Essential for proteolytic processing of an antiapoptotic form of OPA1 which prevents the release of mitochondrial cytochrome c in response to intrinsic apoptotic signals (PubMed:16839884). Required for the maturation of PINK1 into its 52kDa mature form after its cleavage by mitochondrial-processing peptidase (MPP) (By similarity). Promotes changes in mitochondria morphology regulated by phosphorylation of P-beta domain (By similarity). Cleaves type-1 transmembrane domains using a catalytic dyad composed of serine and histidine that are contributed by different transmembrane domains. Interacts with PSEN1 and PSEN2 (By similarity). Binds OPA1. Translocated into the nucleus by an unknown mechanism (By similarity). P-beta is proteolytically processed (beta-cleavage) in a PARL-dependent manner. Mice develop normally until 4 weeks of age. They show subsequent progressive growth retardation, atrophy of muscle, spleen, and thymus as well as severe apoptosis of T and B lymphocytes leading to premature death between 8-12 weeks of age. Mouse embryonic fibroblasts lacking Parl show high susceptibility to intrinsic apoptotic signals. This defect can be complemented by Parl or a soluble form of Opa1. Belongs to the peptidase S54 family.