The presence and orientation of ecto‐5'‐nucleotidase in rat liver lysosomes

Purified rat liver lysosomes contained 5'-nucleotidase activity which was 92 ± 2% [4] latent. This latency was lost in response to a permeant sugar at a similar rate to that of the lysosomal marker enzyme β-N-acetyl-glucosaminidase indicating that the 5'-nucleotidase was genuinely located in the lysosome and not a plasma membrane contaminant. Lysosomal 5'-nucleotidase exhibited the following properties characteristic of ecto-5'-nucleotidase inhibition by specific polyclonal antibodies: binding to a monoclonal antibody; inhibition by 1 αβ-methylene ADP; immunoreactive subunits of 70 and 38 kDa. Lysosomes in addition contained immunoreactive species of intermediate molecular mass.