Transducin subunit stoichiometry and cellular distribution in rod outer segments

Authors

  • James W. Clack,

    Corresponding author
    1. Department of Biology, Indiana University, Purdue University at Indianapolis, 4601 Central Ave., Columbus, IN 47203, USA
      Corresponding author. Tel.: +1 812 348 7266; fax: +1 812 348 7280. jclack@iupui.edu
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  • Matthew L. Springmeyer,

    1. Department of Biology, Indiana University, Purdue University at Indianapolis, 4601 Central Ave., Columbus, IN 47203, USA
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  • Candice R. Clark,

    1. Department of Biology, Indiana University, Purdue University at Indianapolis, 4601 Central Ave., Columbus, IN 47203, USA
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  • Frank A. Witzmann

    1. Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN, USA
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Corresponding author. Tel.: +1 812 348 7266; fax: +1 812 348 7280. jclack@iupui.edu

Abstract

Transducin is a heterotrimeric GTP-binding protein found in the outer segment of vertebrate retinas that links the photoactivation of rhodopsin (R*) with activation of a robust type VI cGMP phosphodiesterase (PDE6). Association of the alpha subunit of Transducin (G αt) with the beta-gamma complex (G βγ) is necessary for interaction of the holoprotein with R* and exchange of a GTP for a previously bound GDP. We have investigated the abundances of the three Transducin subunits by eluting them from bovine rod outer segment membranes by centrifugation under various conditions in vitro. We find that a substantial amount of G βγ is eluted from ROS under conditions that do not elute G αt and that there is an overall three to fourfold molar excess of G βγ to G αt in rod outer segments. These results suggest that the production and/or turnover of G αt, G β, and G γ in the rod outer segment are controlled independently.

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