May play some biological role in the host defense system on the mucous membrane independently of or in cooperation with other substances in airway mucous or bronchial secretions. Plays a role in the proteolytic processing of ACE2. Preferentially cleaves the C-terminal side of arginine residues at the P1 position of certain peptides (By similarity). Isoform 2 may play a key role in regulating adrenal proliferation by specifically cleaving N-POMC. Monomer. Activated by cleavage and secreted. Isoform 1 and isoform 2 are expressed in the esophagus, tongue and trachea. Isoform 2 is also highly expressed in the adrenal cortex and heart. Secreted and retained on the cell surface after secretion. Belongs to the peptidase S1 family.