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Three Forms of Gi Discriminated by Synthetic Peptide Antisera

  • Susanne M. Mumby

Abstract

Two signal transduction pathways that are regulated by guanine nucleotide-binding proteins (G proteins) have been well characterized: the light-stimulated visual cascade and the hormone-sensitive adenylyl cyclase system (for review see Stryer, 1986; Gilman, 1987). Stimulation of retinal cyclic GMP phosphodiesterase by the photoreceptor rhodopsin is mediated by the G protein Gt (also referred to as transducin). Hormone-sensitive adenylyl cyclase is under dual stimulatory and inhibitory control by two other G proteins, Gs and Gi Receptors that stimulate adenylyl cyclase are coupled to the enzyme by Gg, whereas inhibitory receptors are coupled by Gi. These classical G proteins exhibit a characteristic heterotrimeric subunit structure. The ß and γ subunits are tightly associated with each other and in some cases are functionally interchangeable between different α subunits. The α subunits display more structural heterogeneity and functional specificity, and thus they serve to distinguish the different G protein oligomers. The α subunits possess a high-affinity binding site for guanine nucleotides and an intrinsic GTPase activity that are involved in the activation and deactivation of the G protein. Toxins from Vibrio cholerae and Bordetella pertussis are capable of covalently modifying and functionally altering a subunits. Cholera toxin catalyzes the ADP-ribosylation of Gs and Gt. ADP-ribosylation by pertussis toxin blocks activation of Gt and Gi by receptors. Activation of G proteins in detergent solution (and Gt in phospholipid vesicles) by nonhydrolyzable analogs of GTP involves dissociation of the α subunit from βγ. It is the α subunits of Gs and Gts and αt) that stimulate their respective effector enzymes.

Keywords

Adenylyl Cyclase Guanine Nucleotide Pertussis Toxin Bovine Brain Rabbit Liver 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media New York 1989

Authors and Affiliations

  • Susanne M. Mumby
    • 1
  1. 1.Department of PharmacologyUniversity of Texas Southwestern Medical Center at DallasDallasUSA

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