Whereas the cholera toxin ADP-ribosylates the alpha subunit of stimulatory G protein (Gs), thereby blocking GTP hydrolysis, pertussis toxin ADP-ribosylates the alpha subunit of inhibitory G protein (Gi) and prevents interaction with the receptor. What is the effect of these toxins on the concentration of intracellular cAMP? Selected Answer: c They both tend to increase cAMP concentration. Answers: a. Cholera toxin tends to increase cAMP concentration, where as pertussis toxin tends to decrease cAMP concentration. b. Cholera toxin tends to decrease cAMP concentration, whereas pertussis toxin tends to increase cAMP concentration. c. They both tend to increase cAMP concentration. d. They both tend to decrease cAMP concentration.