The glycosylation state of the precursors of the cathepsin B-like proteinase from human malignant ascitic fluid: possible implication in the secretory pathway of these proenzymes.

We have investigated the structure of the carbohydrate moiety of the precursors of the cathepsin B-like proteinase (PCBt). The largest precursor has an apparent molecular size (Mr) of 45-47 Kd and it contains 3 N-linked oligosaccharide chains which were Endo beta N acetylglucosaminidase H (Endo H)-resistant forms. On the other hand, these chains were sequentially removed by Endo beta N acetylglucosaminidase F (Endo F). Both results indicate a complex type structure for these oligosaccharides. As usual in these cases, sialic acids were also found. In the deglycosylated state, PCBt has a Mr value of 36 Kd closely related to the 35.9 Kd Mr for human Pro CB, deduced from the cDNa sequence. These findings may explain the extracellular location of PCBt in malignancy: complex oligosaccharides are in most cases associated with secretory or membrane bound glycoproteins. On the contrary, mannose-rich types are involved in the lysosomal routage.