May be involved in the regulation of serine proteinases present in the brain or extravasated from the blood (By similarity). 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 and loss of this protection results in cell death and sensorineural hearing loss. Forms a complex with the monomeric form of beta-tryptase. Expressed in keratinocytes (at protein level). Highest levels in skeletal muscle. Also found in placenta, cardiac muscle, lung, liver, kidney and pancreas. Expressed in the inner ear hair cells. Expressed abundantly by normal mast cells in different tissues and by mast cells in mastocytoma lesions. The disease is caused by variants affecting the gene represented in this entry. Belongs to the serpin family. Ov-serpin subfamily.