Trypsin-like protease with a narrow substrate specificity. Preferentially hydrolyzes substrates with Pro in the P2 position and Val in the P3 position. Plays a role in fertilization. Hydrolyzes arginyl bonds, preferably with Pro in the P2 position. Inhibited by peptidyl-argininals wth Pro in the P2 position, diisopropyl fluorophosphate, phenylmethanesulfonyl fluoride, leupeptin, antipain, soybean trypsin inhibitor, aprotinin, ovomucoid, valyl-prolyl-arginyl-chloromethane, glycyl-valyl-arginyl-chloromethane, p-aminobenzamidine, benzamidine, zinc chloride and mercuric chloride. Optimum pH is 8.5-9.0. Heterodimer of a heavy chain and either an L1 light chain or an L2 light chain linked by a disulfide bond. Localized on the sperm head. Released into the surrounding seawater in response to the sperm reaction, a large proportion remains associated with the sperm cell surface. Detected in sperm, but not in unfertilized eggs (at protein level). Expressed in gonad, but not in hepatopancreas, intestine or branchial basket. Expression begins about half a month before the start of the spawning season (early December), and continues throughout the spawning season. Belongs to the peptidase S1 family.