Human cathepsin D precursor is associated with a 60 kDa glycosylated polypeptide

Human cathepsin D is synthesized as a 53 kDa precursor. Most of it is segregated into lysosomal compartments and subjected to a proteolytic fragmentation. Using a cross-linking reagent we show that a large proportion of the precursor is associated with a distinct protein which--under denaturing and reducing conditions--is characterized as a 60 kDa glycopeptide. Studies on cells cultured in the presence of drugs known to affect the intracellular transport (deoxynojirimycin, brefeldin A and NH4Cl) indicated that the association with cathepsin D precursor occurs early after the synthesis and is at least partially maintained after secretion.