GTP-binding proteins in luminal and basolateral membranes from pars convoluta and pars recta of rabbit kidney proximal tubule

The GTP-binding proteins on luminal and basolateral membrane vesicles from outer cortex(pars convoluta) and outer medulla (pars recta) of rabbit proximal tubule have been examined. The membrane vesicles were highly purified, as ascertained by electron microscopy, by measurements of marker enzymes, and by investigating segmental-specific transport systems. The [ 35S]GTPγS binding to vesicles, and to sodium cholate-extracted proteins from vesicles, indicated that the total content of GTP-binding proteins were equally distributed on pars convoluta, pars recta luminal and basolateral membranes. The membranes were ADP-ribosylated with [ 32P]NAD + in the presence of pertussis toxin and cholera toxin. Gel electrophoresis revealed, for all preparations, the presence of cholera toxin [ 32P]ADP-ribosylated 42 and 45 kDa Gα, proteins, and pertussis toxin [ 32P]ADP-ribosylated 41 kDa Gα il, 40 kDa Gα 12 and 41 kDa Gα 13 proteins. The 2D electrophoresis indicated that G o's were not present in luminal nor in basolateral membranes of pars convoluta or pars recta of rabbit proximal tubule.