Amino acid sequence of an inducible cysteine proteinase inhibitor (cystatin) from submandibular glands of isoproterenol-treated rats.

We have previously reported the purification of an inducible cysteine proteinase inhibitor from submandibular glands of isoproterenol-treated rats by sequential gel filtration and ion-exchange chromatography [G. S. Bedi (1989) Arch. Biochem. Biophys. 270, 335-343]. This inhibitor is not detected in normal rat tissues but is induced in submandibular glands following beta-adrenergic stimulation of rats. In this study the complete amino acid sequence and the position of disulfide bridges of the purified protein were determined by automated Edman degradation of the protein and its tryptic, chymotryptic, and Staphylococcus aureus V8 protease peptides and were as follows: (sequence; see text) Computer analysis revealed the presence of 40-50% sequence identity between inducible cysteine proteinase inhibitor and cystatins from human saliva, human cystatin C, bovine cystatins, and chicken cystatins, all members of Family 2 cystatins. The inhibitor has little sequence similarity with rat liver and epidermal cysteine proteinase inhibitors, which belong to Family 1 cystatins.