Cystatins of human placenta.

Two low-molecular protein fractions inhibiting cysteine proteases were isolated from human placenta by alkalization to pH 11, acetone fractionation, affinity chromatography on CM-papain-Sepharose 4B, and Sephadex G-75 gel filtration. The results of polyacrylamide gel electrophoresis, isoelectric focusing indicate that one of there fractions in a dimer of cystatins B, and another is a mixture of cystatins A and B.