Serine protease which possesses both gelatinolytic and caseinolytic activities. Shows a preference for Arg in the P1 position. Inhibited by SERPINA5. Forms a heterodimer with SERPINA5 and SERPINE1. Activated by cleavage and secreted. Expression can only be detected in tissues derived from the head and neck, and in skin, prostate and testis. N-glycosylated. Belongs to the peptidase S1 family. It is uncertain whether Met-1 or Met-2 is the initiator.