Serine protease. Hydrolyzes the peptides N-t-Boc-Gln-Ala-Arg-AMC and N-t-Boc-Gln-Gly-Arg-AMC and, to a lesser extent, N-t-Boc-Ala-Phe-Lys-AMC and N-t-Boc-Val-Leu-Lys-AMC. Has a preference for substrates with an Arg instead of a Lys residue in position P1 (By similarity). Inhibited by serine proteinase inhibitor 4-(2-aminoethyl)-benzenesulfonyl fluoride, but not with EDTA or E-64. Not attached to membranes. The first serine protease domain is catalytically active, whereas the second domain lacks the essential His residue of the catalytic triad at position 363, and the third domain lacks the essential Asp residue of the catalytic triad at position 673. The second and third domains are therefore predicted to be inactive. The 3 protease domains are not proteolytically cleaved. N-glycosylated. Belongs to the peptidase S1 family.