title: G protein-effector coupling: binding of rod phosphodiesterase inhibitory subunit to transducin.
abstract: The cyclic GMP phosphodiesterase of retinal rods is composed of three distinct polypeptides: alpha (90 kDa), beta (86 kDa), and gamma (10 kDa). In this multimeric form, the enzyme is inhibited. Its activity is stimulated by the interaction with the GTP-bound form of the T alpha subunit of transducin and reversed upon the recombination of the inhibitory gamma subunit with the catalytic alpha beta subunit. We show here by a novel coimmunoprecipitation technique that the gamma subunit, but not the alpha beta subunit, forms a 1:1 complex with T alpha. The binding of gamma to T alpha is nucleotide-dependent and is facilitated by GTP gamma S or Gpp(NH)p. This study provides convincing evidence that the T alpha-GTP subunit of transducin stimulates phosphodiesterase activity by binding to gamma and physically carrying it away from alpha beta.
authors.affiliation: Jules Stein Eye Institute, University of California School of Medicine, Los Angeles 90024.
authors.forename: B K
authors.initials: BK
authors.lastname: Fung
authors.forename: I
authors.initials: I
authors.lastname: Griswold-Prenner
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D004789:Enzyme Activation; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D006165:Guanylyl Imidodiphosphate / Q000378:metabolism; D066298:In Vitro Techniques; D010786:Photoreceptor Cells / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D013873:Thionucleotides / Q000378:metabolism; D015293:Transducin / Q000378:metabolism*
chemical_list: D013873:Thionucleotides; D006165:Guanylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D015293:Transducin