Serase-1 and serase-2 are serine proteases that hydrolyze the peptides N-t-Boc-Gln-Ala-Arg-AMC and N-t-Boc-Gln-Gly-Arg-AMC. In contrast, N-t-Boc-Ala-Phe-Lys-AMC and N-t-Boc-Ala-Pro-Ala-AMC are not significantly hydrolyzed. Inhibited by serine protease inhibitors PMSF and 4-(2-aminoethyl)benzenesulfonyl fluoride, but not by EDTA. Expressed in fetal human tissues, such as kidney, liver, lung and brain, and in a variety of tumor cell lines. Weakly expressed in adult tissues including skeletal muscle, liver, placenta and heart. The serine protease 1 and 2 domains are catalytically active, whereas the serine protease 3 domain lacks the essential Ser residue of the catalytic triad at position 1009 and is predicted to be inactive. Proteolytically cleaved to generate 3 independent serine protease chains. The cleaved chains may remain attached to the membrane thanks to disulfide bonds. It is unclear whether cleavage always takes place. Belongs to the peptidase S1 family. Aberrant splicing.