Sorting receptor that directs prohormones to the regulated secretory pathway. Acts also as a prohormone processing enzyme in neuro/endocrine cells, removing dibasic residues from the C-terminal end of peptide hormone precursors after initial endoprotease cleavage. Release of C-terminal arginine or lysine residues from polypeptides. Binds 1 zinc ion per subunit. Interacts with secretogranin III/SCG3. Associated with the secretory granule membrane through direct binding to lipid rafts in intragranular conditions. Expressed in brain, heart and anterior pituitary gland. Also expressed in pancreatic islets and adrenal gland. An autoantigen recognized by serum of pretype I diabetes. Belongs to the peptidase M14 family.