Serine protease inhibitor which exhibits anti-trypsin activity (PubMed:3428272, PubMed:14645103, PubMed:22228629). In the pancreas, protects against trypsin-catalyzed premature activation of zymogens (PubMed:16083722). In the male reproductive tract, binds to sperm heads where it modulates sperm capacitance by inhibiting calcium uptake and nitrogen oxide (NO) production (PubMed:9828198, PubMed:14645103, PubMed:16083722, PubMed:22228629). In the genital tract, expressed only in male accessory glands including seminal vesicle, coagulating gland and prostate. In the seminal vesicle, not expressed during prepubertal stages; expression coincides with maturation. By androgens in adult male sex accessory glands. Expressed constitutively in pancreas. Lethal with no survival past two weeks of age. Animals are small and show severe, progressive degeneration of pancreatic tissue associated with autophagic cell death.