PRSS35, although related to the peptidase S1 family, lacks the conserved active Ser residue in position 346 which is replaced by a Thr, suggesting that it has no protease activity. This Ser to Thr substitution may play an important role in determining a unique pattern of substrate specificity for PRSS35. Alternatively, this substitution may yield an inactive protease that binds to specific substrates, thus protecting them from proteolysis. The Mouse Prss35 gene is selectively expressed in the ovary and it's expression prior to ovulation is, in part, regulated by progesterone. PRSS35 may be involved in ovulation and the formation and regression of the corpus luteum.