Purification properties and specificity of cathepsin D from Cyprinus carpio.

Abstract Cathepsin D was purified 750-fold from a homogenate of Cyprinus carpio muscles. The purified enzyme has a molecular weight of 36,000, is inhibited by pepstatin and is active between pH 2.7 and 3.7 when tested on hemoglobin as the substrate. It consists of two isoenzymes with pls of 5.65 and 6.1, respectively. The mode of cleavage of the β chain of oxidized insulin was determined by analysis of the N-terminal amino acids of the cleaved peptides. The major points of cleavage of the β chain of oxidized insulin are 56% at Tyr 16 -Leu 17 and 40% at Phe 25 -Tyr 26 . The minor points of cleavage are at Leul 15 -Tyr 16 ,Phe 24 -Phe 25 , Gly 23 -Phe 24 , Leu 11 -Valu 12 , Ala 14 -Leu 15 and Gln 4 -His 5 .