Characteristics of the Calcium‐Mediated Mechanism Activating Adenylate Cyclase in Trypanosoma brucei

Abstract

1 The adenylate cyclase of bloodstream forms of Trypanosoma brucei is regulated by Ca²⁺. 2 The Ca²⁺-stimulated activity is not inhibited by trifluperazine, tentatively suggesting that the stimulation may not be mediated by calmoduhn. 3 The Ca²⁺-binding site of tile receptor regulating the adenylate cyclase is buried within the hydrophobic region of the plasma membrane and is not exposed to either the inner or the outer aqueous phase bounding the membrane in unstimulated cells. 4 The response of the adenylate cyclase to stimulation by Ca²⁺ within the membrane is a transient increase in activity followed by a period of ‘down regulation’. 5 The ‘down regulation’ of the adenylate cyclase also occurs by a Ca²⁺-dependent mechanism.