Binding of monoclonal antibody to cathepsin M located on the external surface of rabbit lysosomes.

A monoclonal antibody raised against rabbit liver cathepsin M binds to intact rabbit liver lysosomes. The binding is specific and is abolished by treating the lysosomes with trypsin, which has previously been shown to digest the membrane-bound cathepsin M [S. Pontremoli, E. Melloni, M. Michetti, F. Salamino, B. Sparatore, and B. L. Horecker (1982) Biochem, Biophys. Res. Commun. 106, 903-909]. Rabbit liver lysosomes are adsorbed onto Sepharose 4B coupled to anti-cathepsin M, but not to Sepharose 4B itself or to Sepharose coupled to a nonspecific antibody. The results confirm the location of membrane-bound cathepsin M on the outer surface of the lysosomal membrane.