HETEROGENEITY OF HEPATIC PROTEIN-TYROSINE PHOSPHATASES

We have identified multiple members of the protein tyrosine phosphatas e family in three subcellular compartments from rat liver; membrane, c ytoskeleton and cytosol. Characterization based on substrate specifici ty, size, and reactivity with an anti-peptide antiserum against human placental PTP1B indicate the presence of at least three PTPases in Tri ton X-100 extracts of particulate membranes. Of these, one of 600 kDa possesses characteristics of a transmembrane, receptor-like enzyme. A fourth particulate PTPase (70 kDa) represents a distinct cytoskeletal PTPase. Cytosol contains one main PTPase species which was detected as a 41 kDa protein in Western immunoblots. These data indicate the exis tence of multiple hepatic PTPases whose differences in structure and s ubcellular localization may reflect functional heterogeneity.