This protein called 'barrier activity' is excreted by yeast cells mating type a. It is probably a protease that cleaves alpha-factor and thus acts as an antagonist of this mating pheromone and establishes optimal pheromone concentration for conjugation. Selective cleavage of 6-Leu-|-Lys-7 bond in the pheromone alpha-mating factor. By alpha factor. It is found only in a mating type cells. Present with 672 molecules/cell in log phase SD medium. Belongs to the peptidase A1 family.