Biochemical characterization of cathepsin D from the mussel Lamellidens corrianus.

Abstract A lysosomal cathepsin D (EC 3.4.23.5) was purified to homogeneity from the soft tissues of the fresh water mussel ( Lamellidens corrianus ) by pepstatin A affinity chromatography. The purified enzyme is a glycoprotein and migrates as a single protein species in native PAGE and shows a single band in SDS-PAGE corresponding to a molecular mass of ~ 43 kDa. Under both these conditions cathepsin D hydrolyzes hemoglobin as shown by zymogram analysis. The purified enzyme cross-reacts with an antiserum to purified starfish ( Asterias rubens ) cathepsin D. Additionally, the enzyme was recognized by the starfish lysosomal enzyme targeting receptors (mannose 6-phosphate receptors: MPR 300 and 46) in ligand blot analysis. The K M value of the purified enzyme with hemoglobin is 1.5 mM. pH and temperature optimum for the enzyme are 3.5 and 60 °C respectively.