HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Gray-Keller, M. P. Articles by Bownds, M. D. Search for Related Content PubMed PubMed Citation Articles by Gray-Keller, M. P. Articles by Bownds, M. D. Social Bookmarking                      What's this?

J. Biol. Chem., Vol. 265, Issue 25, 15323-15332, Sep, 1990

Transducin activation in electropermeabilized frog rod outer segments is highly amplified, and a portion equivalent to phosphodiesterase remains membrane-bound

MP Gray-Keller, MS Biernbaum and MD Bownds
Neuroscience Training Program, University of Wisconsin, Madison 53706.

An electropermeabilized preparation of frog retinal rod outer segments (ROS) has been developed to examine the light sensitivity and amplification of visual transduction reactions in a minimally disturbed environment. Electropermeabilized ROS are indistinguishable from whole and osmotically intact ROS in the light microscope and retain 3-fold more protein than mechanically disrupted ROS. They differ from mechanically fragmented ROS in several respects. Illumination results in more amplified activation of the GTP-binding protein transducin (Gt) than previously observed: bleaching as little as approximately 1 rhodopsin molecule (Rho*) in every 10 disks within a single ROS activates 37,000 molecules of Gt per Rho*, equivalent to 70% of the light-activatable Gt present on a single disk face. This amplification is maintained over approximately 1 decade of light intensity but drops sharply as disk faces begin to absorb a second photon. Lower amplification is observed in fragmented ROS and derives from the fact that physical disruption of ROS causes Gt to bind GTP and elute from the membrane, thus decreasing the amount remaining and available for light activation. Illumination of electropermeabilized ROS in the presence of GTP or of the nonhydrolyzable substrate guanosine 5'-(gamma- thio)triphosphate (GTP gamma S) causes redistribution of Gt: an amount (approximately 20 mmol/mol Rho) equivalent to the amount of inhibitory gamma subunit of phosphodiesterase (PDE) remains internal and bound to nucleotide, and the remaining activated Gt diffuses out in a manner graded with light intensity. This suggests that PDE activation by Gt alpha may not require dissociation of Gt alpha bound to the gamma subunit of PDE in a form than can elute from ROS. Two further differences between electropermeabilized and mechanically disrupted ROS are noted: the addition of ATP to electropermeabilized ROS does not affect the light sensitivity or kinetics of the GTP binding reaction, and a specificity for light-induced GTP versus GDP binding is observed.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				E. Hessel, M. Heck, P. Muller, A. Herrmann, and K. P. Hofmann Signal Transduction in the Visual Cascade Involves Specific Lipid-Protein Interactions J. Biol. Chem., June 13, 2003; 278(25): 22853 - 22860. [Abstract] [Full Text] [PDF]

				M. J. Paglia, H. Mou, and R. H. Cote Regulation of Photoreceptor Phosphodiesterase (PDE6) by Phosphorylation of Its Inhibitory gamma Subunit Re-evaluated J. Biol. Chem., February 8, 2002; 277(7): 5017 - 5023. [Abstract] [Full Text] [PDF]