Thiol protease. Has dipeptidylpeptidase activity. Can act as both an exopeptidase and endopeptidase. Can degrade glucagon. Plays a role in the generation of cytotoxic lymphocyte effector function. Release of an N-terminal dipeptide, Xaa-Yaa-|-Zaa-, except when Xaa is Arg or Lys, or Yaa or Zaa is Pro. Binds 1 Cl(-) ion per heavy chain. Tetramer of heterotrimers consisting of exclusion domain, heavy- and light chains. Broadly distributed, but higher levels found in lung, liver, kidney and spleen. Lower levels found in testis and brain. Belongs to the peptidase C1 family.