the site of action of the protein appears to be at the level of the guanine nucleotide regulatory ( g ) protein of the plasma membrane adenylate cyclase complex , as the factor , cooperatively with gtp , also permitted cholera toxin to adp-ribosylate ( from 32p-labeled nad ) two integral membrane proteins that migrated on sds-polyacrylamide gel electrophoresis gels with the mobilities ( mr approx . 46 000 and 48 000 ) generally observed for the guanine nucleotide regulator protein subunits .
C0018353
gtp
C0018328
guanine nucleotide