Purification and characterization of an inducible cysteine proteinase inhibitor from submandibular glands of isoproterenol-treated rats.

A low-molecular-weight protein, induced in rats following prolonged isoproterenol treatment, has been purified from rat submandibular glands by chromatography on columns of Sepharose CL-6B, DEAE-Sepharose CL-6B, and Sephadex G-75. The purified protein is homogeneous based on gel electrophoresis and Ouchterlony double diffusion. The molecular weight of the purified protein was 14,000 and 15,500 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration on a Superose 12 column, respectively. This protein contains 31% glutamic acid/glutamine and aspartic acid/asparagine, 3.6% cysteine, and 2.5% proline. This protein is shown to be an inhibitor of several cysteine proteinases, papain and ficin being inhibited very strongly in approximately 1:1 molar ratio of enzyme to inhibitor. The protein is not detected in normal rat tissues but is induced in submandibular and sublingual glands even after 1 day of isoproterenol treatment of rats as early as 7 days after birth. Based on cysteine proteinase inhibitor activity, molecular size, and chemical composition this protein appears to belong to the cystatin superfamily.