Amphiphile-mediated activation of soluble adenylate cyclase of Bordetella pertussis

The adenylate cyclase activity of Bordetella pertussis culture supernatants is activated 3- to 10-fold by various amphiphiles including many classes of phospholipids and nonionic detergents. Gangliosides are inhibitory. The stimulation affects the V_max and not the K_m. Neither the nature of the polar head group, the length of the fatty acid chains, nor the hydrophile-lipophile balance (in the Triton X series) are major determinants for activation. Short-chain lecithins activate as monomers, whereas long-chain lecithins activate only above the critical micelle concentrations, suggesting high-affinity hydrophobic binding sites. Judged by EGTA inhibition, the amphiphile-mediated activation requires Ca²⁺ in the absence of calmodulin. In addition, amphiphiles sensitize the adenylate cyclase to Ca²⁺/calmodulin and are also synergistic with calmodulin for maximal stimulation.