Serine endoprotease that processes various proproteins by cleavage at paired basic amino acids, recognizing the RXXX[KR]R consensus motif. Likely functions in the constitutive secretory pathway, with unique restricted distribution in both neuroendocrine and non-neuroendocrine tissues. The PACE4A-I precursor protein seems to exist in the reticulum endoplasmic as both a monomer and a dimer-sized complex whereas mature PACE4A-I exists only as a monomer, suggesting that propeptide cleavage affects its tertiary or quaternary structure. Interacts (immature form including the propeptide) with RCN3; probably involved in the maturation and the secretion of PCSK6 (PubMed:16433634). Not secreted, remains probably in zymogen form in endoplasmic reticulum. Not secreted, remains probably in zymogen form in endoplasmic reticulum. Retained intracellularly probably through a hydrophobic cluster in their C-terminus. Retained intracellularly probably through a hydrophobic cluster in their C-terminus. Each PACE4 isoform exhibits a unique restricted distribution. Isoform PACE4A-I is expressed in heart, brain, placenta, lung, skeletal muscle, kidney, pancreas, but at comparatively higher levels in the liver. Isoform PACE4A-II is at least expressed in placenta. Isoform PACE4B was only found in the embryonic kidney cell line from which it was isolated. Isoform PACE4C and isoform PACE4D are expressed in placenta. Isoform PACE4E-I is expressed in cerebellum, placenta and pituitary. Isoform PACE4E-II is at least present in cerebellum. The propeptide domain acts as an intramolecular chaperone assisting the folding of the zymogen within the endoplasmic reticulum. Isoform PACE4D lacks the propeptide domain. Probably enzymatically inactive. Probably enzymatically inactive. Probably enzymatically inactive. Probably enzymatically inactive. Belongs to the peptidase S8 family.