Characterization of cystatin C from bovine parotid glands: cysteine proteinase inhibition and antiviral properties.

Cystatin C, a low Mr cysteine proteinase inhibitor was isolated from bovine parotid glands by a procedure which includes alkaline treatment of the homogenate, affinity chromatography, gel filtration and ion exchange chromatography. The purified inhibitor has a pl of 8.0 and Mr of 14500. The identity with bovine cystatin C from colostrum was confirmed by N-terminal sequence of the inhibitor and amino acid composition. Cystatin C rapidly (kass = 5.5 x 10(7) M-1s-1) and tightly inhibits papain (Ki = 0.02 nM), whereas its interaction with bovine cathepsin B is substantially weaker (Ki = 4.4 nM). Bovine cystatin C also shows a weak antiviral effect on poliovirus infected human Hela cells.