DISTRIBUTION OF POLYPEPTIDES BINDING GUANOSINE 5'-[GAMMA-[S-35]THIO]TRIPHOSPHATE AND ANTI-(RAS PROTEIN) ANTIBODIES IN LIVER SUBCELLULAR-FRACTIONS - EVIDENCE FOR ENDOSOME-SPECIFIC COMPONENTS

The subcellular distribution in rat liver of polypeptides binding guanosine 5'-[γ-[35S]thio]triphosphate ([35S]GTP[S]) and seven antibodies against ras oncoproteins was evaluated. Multiple low-M(r) (21,000-28,000) GTP-binding proteins were detected, but their relative distribution among the membrane fractions varied. A more specific compartmentation of polypeptides which bind antibodies generated against ras proteins was evident, with an M(r)-28,000 polypeptide and a probable M(r)-56,000 dimer, identified by six of the antibodies tested, being confined mainly to endosomes. An M(r)-23,000 polypeptide was detected by some of the antibodies in all of the membrane fractions, but especially in the plasma membranes.