Seminal fluid protease which is required for cleavage and probably also activation of the metalloprotease Semp1 (PubMed:22253601, PubMed:24514904). Also required for a number of female post-mating responses independent of Semp1 including egg laying and sperm usage (PubMed:22253601). Secreted into seminal fluid. Produced in the male accessory glands and secreted into seminal fluid. Undergoes cleavage in the male during mating with a cleaved product detected in the ejaculatory duct and/or bulb of males by 8-10 minutes after the start of mating. Further cleavage occurs in the mated female. RNAi-mediated knockdown in males results in a number of effects in females mated with these males including impaired processing of the metalloprotease Semp1 and the accessory gland proteins Acp26Aa and Acp36DE, lower levels of egg laying after the first day post-mating, higher rates of sexual receptivity to subsequent males and failure to release stored sperm from the female seminal receptacle. Belongs to the peptidase S1 family. Extended N-terminus.