Purification of the cystatin C-like inhibitors from urine of nephropathic rats.

Two cysteine proteinase inhibitors of the cystatin C type have been purified from urine of sodium chromate-treated rats. Both strongly inhibit papain as well as rat liver cathepsin L (Ki less than 10(-11) M) whereas rat liver cathepsins B and H are inhibited to a lesser extent. They differ by their apparent molecular mass of 17 kDa and 22 kDa and by their isoelectric point greater than or equal to 9.5 and 7.7 respectively. These two molecules share complete immunochemical identity and are precipitated by antibodies directed against human cystatin C but not by anti rat thiostatin and anti rat H-kininogen antibodies. They are also found in large amounts in seminal vesicles where they represent most of the cysteine proteinase inhibitory capacity.