GDP does not support activation of adenylate cyclase nor ADP-ribosylation of a guanine nucleotide binding protein by cholera toxin.

The actions of cholera toxin (i.e., activation of adenylate cyclase and ADP-ribosylation of a guanine nucleotide binding protein in purified membranes from rat liver) were GTP dependent. Neither of these actions of cholera toxin was reproduced with GDP. Simultaneous addition of ATP and MgCl2 along with GDP allowed cholera toxin to exert these actions. The role of GDP in adenylate cyclase regulation was discussed.