The Role of β, γ-Subunits of Guanine Nucleotide Binding Proteins in Control of a Reconstituted Signal Transmission Chain Containing Purified Components of the Adenylate Cyclase System

Abstract

The properties of a reconstituted signal transmission chain using purified β₁-adrenoceptor (R), G-protein subunits (G) and adenylate cyclase (C) in lipid vesicles are described. This assay system was used to test β,γ-subunits of different origin with respect to their effects on R·G and R·G·C coupling and on the functional properties of G_sα and G_iα. The findings reported here point to large differences in the efficacy of β,γ-subunits from different sources assessed by deactivation of [AlF₄]^- activated rabbit liver G_s and pertussis toxin-catalyzed ADP-ribosylation of bovine neutrophil G_α. This is explained by differences in the interaction domains of the interacting subunits. Furthermore, the sensitivity of R·G and R·G·C coupling to inhibition by β,γ-sub-units was greater than the effects of β,γ-subunits on hormonally activated GTPase activity of G_s. One of the consequences of differential inhibition of R·G·C coupling is an amplified response of the signal transmission chain to hormonal activation. This is in agreement with observations reported by Cerione et al. (1)