Inhibitor of cathepsin G, kallikrein-8 and thrombin. May play an important role in the inner ear in the protection against leakage of lysosomal content during stress. May be involved in the regulation of serine proteinases present in the brain or extravasated from the blood (By similarity). Forms a complex with the monomeric form of beta-tryptase. Belongs to the serpin family. Ov-serpin subfamily.