Occurrence of cathepsin D isozymes with different specificities in monkey skeletal muscle

Summary Cathepsin D was highly purified from the skeletal muscle of Japanese monkey ( Macaca fuscata fuscata ) by a procedure including affinity chromatography on concanavalin A-Sepharose and pepstatin-Sepharose, and then resolved into ten isozymes (A through J) by isoelectric focusing. When examined for specificity toward oxidized insulin B chain, isozyme A was highly specific and cleaved exclusively the Leu 15 -Tyr 16 bond, whereas isozyme F was less specific, cleaving the Leu 15 -Tyr 16 and Glu 13 -Ala 14 bonds, with slower cleavages at several other bonds. These results demonstrate for the first time the occurrence of isozymes with different specificities among cathepsin D isozymes obtained from a single source.