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. Belongs to the peptidase M14 family.