Plays an important role in the degradation of some oligopeptides. Release of an N-terminal dipeptide, Xaa-Yaa-|-, preferentially when Yaa is Ala or Pro. Substrates are oligopeptides, preferentially tripeptides. Optimum pH is 5.5. Has low activity at pH 7 and is inactive at pH 8. Homodimer. Detected in seminal plasma (at protein level). N-glycosylated. Belongs to the peptidase S28 family.