Two cystatins (cst-I and cst-II) were purified from crucian carp eggs by
acidification, and chromatography on CM-Sepharose and Sephacryl S-100 HR.
The molecular masses of cst-I and cst-II analyzed on SDS-PAGE were 11.9 and
14.4 kDa under reducing condition, while those were 13.5 and 12.7 kDa under
non-reducing condition. The cst-I and cst-II were stable after 30 min of
incubation respectively within 60°C and 50°C. No significant loss in the
inhibitory activity of both cst at pH range of 4-11. They could affect the
proteolysis of papain, cathepsin L and bromelain, but could not inhibit
cathepsin B and trypsin. The partial N-terminal amino acid sequences of both
cst inhibitors were homologous and that of cst-I was recognized as NH2-
AGIPGGLVDADINDADVQ. This fragment shared 88.9% identity to common
carp cystatin and 44.4-55.6% to cystatins of other aquatic animals. Therefore,
the two cst inhibitors were members of family 2 cystatin.