title: A GTPase-accelerating factor for transducin, distinct from its effector cGMP phosphodiesterase, in rod outer segment membranes.
abstract: Hydrolysis of GTP by the photoreceptor G protein transducin (Gt alpha) was found to occur with kinetics identical to the inactivation of its effector cGMP phosphodiesterase (PDE), but was too slow (tens of seconds) in dilute rod outer segment (ROS) suspensions to account for subsecond recovery of the light response. Raising the concentration of ROS membranes increased the rates of GTP hydrolysis and PDE inactivation in parallel as much as 6-fold. Holo-PDE and its gamma subunit had weak effects on GTPase kinetics (< 1.6-fold and < 1.3-fold, respectively). ROS membranes stripped of PDE retained approximately 90% of a GTPase accelerating activity that was protease sensitive, indicating that they contain a GTPase-accelerating factor distinct from PDE.
authors.affiliation: Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas.
authors.forename: J K
authors.initials: JK
authors.lastname: Angleson
authors.forename: T G
authors.initials: TG
authors.lastname: Wensel
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D004789:Enzyme Activation / Q000187:drug effects; D020690:GTPase-Activating Proteins; D006160:Guanosine Triphosphate / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D015293:Transducin / Q000378:metabolism*
chemical_list: D020690:GTPase-Activating Proteins; D010726:Phosphodiesterase Inhibitors; D011506:Proteins; D006160:Guanosine Triphosphate; D010727:Phosphoric Diester Hydrolases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D015293:Transducin