Neuron
Volume 11, Issue 5, November 1993, Pages 939-949
Journal home page for Neuron

Article
A GTPase-accelerating factor for transducin, distinct from its effector cGMP phosphodiesterase, in rod outer segment membranes

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Abstract

Hydrolysis of GTP by the photoreceptor G protein transducin (G) 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 γ subunit had weak effects on GTPase kinetics (<1.6-fold and <1.3-fold, respectively). ROS membranes stripped of PDE retained ∼90% of a GTPase accelerating activity that was protease sensitive, indicating that they contain a GTPase-accelerating factor distinct from PDE.

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