Ubiquitous endoprotease within constitutive secretory pathways capable of cleavage at the RX(K/R)R consensus motif (PubMed:18713856). Mediates processing of TGFB1, an essential step in TGF-beta-1 activation (By similarity). Converts through proteolytic cleavage the non-functional Brain natriuretic factor prohormone into its active hormone BNP(1-45) (By similarity). By mediating processing of accessory subunit ATP6AP1/Ac45 of the V-ATPase, regulates the acidification of dense-core secretory granules in islets of Langerhans cells (PubMed:18713856). Release of mature proteins from their proproteins by cleavage of -Arg-Xaa-Yaa-Arg-|-Zaa- bonds, where Xaa can be any amino acid and Yaa is Arg or Lys. Releases albumin, complement component C3 and von Willebrand factor from their respective precursors. Binds 3 calcium ions per subunit. Inhibited by the not secondly cleaved propeptide. Inhibited by m-guanidinomethyl-phenylacetyl-Arg-Val-Arg-(amidomethyl)-benzamidine (m-guanidinomethyl-Phac-RVR-Amb) and 4-guanidinomethyl-phenylacetyl-Arg-Tle-Arg-4-amidinobenzylamide (MI-1148). Inhibited by Decanoyl-Arg-Val-Lys-Arg-chloromethylketone (decanoyl-RVKR-CMK). Inhibited by heparin/heparan sulfate-binding. Interacts with FLNA (PubMed:9412467). Binds to PACS1 which mediates TGN localization and connection to clathrin adapters (By similarity). Shuttles between the trans-Golgi network and the cell surface. Propeptide cleavage is a prerequisite for exit of furin molecules out of the endoplasmic reticulum (ER). A second cleavage within the propeptide occurs in the trans Golgi network (TGN), followed by the release of the propeptide and the activation of furin. Seems to be expressed ubiquitously (PubMed:2266110). Expressed in islets of Langerhans (PubMed:18713856). Contains a cytoplasmic domain responsible for its TGN localization and recycling from the cell surface. The inhibition peptide, which plays the role of an intramolecular chaperone, is autocatalytically removed in the endoplasmic reticulum (ER) and remains non-covalently bound to furin as a potent autoinhibitor. Following transport to the trans Golgi, a second cleavage within the inhibition propeptide results in propeptide dissociation and furin activation. Phosphorylation is required for TGN localization of the endoprotease. In vivo, exists as di-, mono- and non-phosphorylated forms. Conditional knockout in pancreas causes mild glucose intolerance (PubMed:18713856). Insulin secretion by islets of Langerhans cells is reduced (PubMed:18713856). In islets of Langerhans cells, processing of pro-proteins including Pcsk2, Ins2/proinsulin II and Gcg/proglucagon and acidification of dense-core secretory granules are reduced (PubMed:18713856). Islets of Langerhans are normal (PubMed:18713856). Belongs to the peptidase S8 family. Furin subfamily.