Serine protease with chymotrypsin-like cleavage specificity. Shows activity towards casein, gelatin, IGFBP3 and fibronectin but not towards laminin or collagens I and IV. Does not hydrolyze kininogin to release Lys-bradykinin. Strongly inhibited by protease inhibitors diisopropyl fluorophosphate, phenylmethanesulfonyl fluoride and SBTI. Expressed in testis and submaxillary gland. Not expressed in heart, brain, spleen, lung, liver, muscle, kidney and ovary. In the testis, expression localized specifically to Leydig cells in the interstitial tissues. Detectable in testis 4 weeks after birth, becoming more prominent thereafter. Belongs to the peptidase S1 family. Kallikrein subfamily.