title: Interactions between the subunits of transducin and cyclic GMP phosphodiesterase in Rana catesbiana rod photoreceptors.
abstract: In bullfrog (Rana catesbiana) rods the activity of cyclic GMP (cGMP) phosphodiesterase was stimulated 10 times by washing disc membranes with an isotonic, GTP-containing buffer. This stimulation was maintained following hydrolysis of GTP and after removal of guanine nucleotides. At least 60-70% of the inhibitory gamma subunit of cGMP phosphodiesterase (P gamma) was physically released from membranes by these washing procedures. When cGMP phosphodiesterase was activated by a hydrolysis-resistant GTP analogue, P gamma was found in the supernatant complexed with the transducin alpha subunit (T alpha) using three chromatography systems. When GTP was used to activate cGMP phosphodiesterase, P gamma was also found in the supernatant complexed with GDP.T alpha. This complex was also isolated using the same three chromatography systems, indicating that P gamma remained tightly bound to T alpha even after bound GTP was hydrolyzed. Interaction with the beta,gamma subunits of transducin, which remained associated with disc membranes, was required for the release of P gamma from the GDP.T alpha complex, which resulted in the deactivation of active cGMP phosphodiesterase. We conclude that during activation of cGMP phosphodiesterase, P gamma is complexed with T alpha (both GTP and GDP forms) in the supernatant and that, following GTP hydrolysis, beta,gamma subunits of transducin are necessary for the release of P gamma from the complex and the resulting inactivation of cGMP phosphodiesterase in frog photoreceptors.
authors.affiliation: Life Sciences Division, Los Alamos National Laboratory, New Mexico 87545.
authors.forename: A
authors.initials: A
authors.lastname: Yamazaki
authors.forename: F
authors.initials: F
authors.lastname: Hayashi
authors.forename: M
authors.initials: M
authors.lastname: Tatsumi
authors.forename: M W
authors.initials: MW
authors.lastname: Bitensky
authors.forename: J S
authors.initials: JS
authors.lastname: George
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D010786:Photoreceptor Cells / Q000378:metabolism*; D011485:Protein Binding; D011892:Rana catesbeiana; D013873:Thionucleotides / Q000378:metabolism; D015293:Transducin / Q000302:isolation & purification / Q000378:metabolism*; D014357:Trypsin / Q000494:pharmacology
chemical_list: D046911:Macromolecular Substances; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D014357:Trypsin; D015293:Transducin