Guanine nucleotide dependent and independent reconstitution of G‐proteins with adenylate cyclase: stimulation or attenuation of the enzyme by Gi α subunits

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Abstract
The α subunits of five members of the Gi family of bovine brain proteins were reconstituted with adenylate cyclase in phospholipid vesicles. Our results support both the views that much of the inhibition of the enzyme by Gi is due to the action of its liberated βγ subunits, and that the α subunits themselves interact with the enzyme. Inhibition of basal or Gs‐stimulated adenylate cyclase activity is small or undetectable by a subunits of Go, Go∗ and Gi‐2B. On the other hand, adenylate cyclase activity is stimulated by the α subunits of Gi‐1 and Gi‐2A. The G proteins act in the absence of added GTP when reconstituted with phospholipids of low but not high fluidity.