What does pertussis toxin do to adenylate cyclase?

Pertussis toxin, produced by the bacterium Bordetella pertussis, primarily functions by modifying and inhibiting the activity of a specific class of G-proteins within host cells. When pertussis toxin is internalized by the host cell, it catalyzes the ADP-ribosylation of the G-protein Gi, which plays a crucial role in the regulation of adenylate cyclase.

Adenylate cyclase is an enzyme responsible for converting ATP into cyclic AMP (cAMP). Normally, Gi proteins inhibit adenylate cyclase activity; however, when pertussis toxin modifies Gi, it prevents its inhibitory effect. As a result, adenylate cyclase activity becomes uncontrolled, leading to an increase in cAMP levels within the cell.

The correct choice highlights the inhibition of adenylate cyclase as the consequence of this toxin's action on the G-proteins rather than any direct activation or stimulation of adenylate cyclase itself. This mechanism contributes to the pathophysiological effects of whooping cough, including excessive mucus production and bronchoconstriction.