Characterization of cystatin c from bovine parotid glands: Cysteine proteinase inhibition and antiviral properties

Cystatin C, a low M(r) 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 pI of 8.0 and M(r) of 14 500. The identity with bovine cystatin C from colostrum was confirmed by N-terminal sequence of the inhibitor and amino acid composition. Cystatin C rapidly (k(ass) = 5.5 x 10(7) M(-1) s(-1)) and tightly inhibits papain (K-i = 0.02 nM), whereas its interaction with bovine cathepsin B is substantially weaker (K-i = 4.4 nM). Bovine cystatin C also shows a weak antiviral effect on poliovirus infected human Hela cells.