<prompt> Mechanism of action of pertussis toxin is all except:Act by ADP ribosylation of GI subunitIncrease in calciumAct by decreasing GTPB subunit having ADP ribosylating activity  <response>: Ans. is a i.e., Act by ADP ribosylation of GI subunitRef: Harrison, 19the, p. 1021 and Ananthanarayan, 9the, p. 333Pertussis toxin PT - Most imp. Virulence factor composed of 2 subunits A and B like cholera toxin. A subunit having ADP ribosylation activity of G protein - cAMP - responsible for several biological effects like T cell mitogeni- city, Hemagglutination, Adhesion to respiratory ciliated cells, induction of leukocytosis, histamine sensitizer. 