title: Alpha-subunits of Ns are released from the plasma membrane following cholera toxin activation.
abstract: Cholera toxin (CT) and islet-activating protein (IAP, a Bordetella pertussis toxin) were employed to test the hypothesis that GTP-binding regulatory proteins are released from plasma membranes to a greater extent when 'activated' than when 'inactivated'. CT, which activates Ns (the stimulatory GTP-binding regulatory protein of the adenylate cyclase system), catalyzed the incorporation of radioactivity from [32P]NAD into 45 and 47.5 kDa peptides associated with rat liver plasma membranes. Following ADP-ribosylation and centrifugation at 100000 X g for 1 h, approx. 30-35% of these CT-labelled peptides were no longer associated with the plasma membranes, but were recovered from the supernatant fraction. IAP, which inactivates Ni (the inhibitory GTP-binding regulatory protein of the adenylate cyclase system) catalyzed the incorporation of radioactivity from [32P]NAD into a 41 kDa peptide associated with the membranes. However, in contrast to the CT-labelled peptides, typically less than 5% of the IAP-labelled peptide was found in the 100000 X g supernatant fraction, but rather was almost exclusively associated with the membrane pellet. The data indicate that the alpha-subunits of Ns are released from the plasma membrane following activation, and support the hypothesis that the beta gamma-subunits act to anchor the alpha-subunits to the plasma membrane.
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D037361:Adenylate Cyclase Toxin; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002772:Cholera Toxin / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D066298:In Vitro Techniques; D009243:NAD / Q000378:metabolism; D037342:Pertussis Toxin; D010761:Phosphorus Radioisotopes; D051381:Rats; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D010761:Phosphorus Radioisotopes; D010566:Virulence Factors, Bordetella; D009243:NAD; D000246:Adenosine Diphosphate Ribose; D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins