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Choleratoxin ADP‐ribosylates transducin only when it is bound to photoexcited rhodopsin and depleted of its nucleotide
Author(s) -
Bornancin Frédéric,
Chabre Marc
Publication year - 1991
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(91)81300-w
Subject(s) - transducin , rhodopsin , nucleotide , chemistry , biophysics , guanine nucleotide exchange factor , microbiology and biotechnology , biology , biochemistry , gtpase , retinal , gene
The sensitivity of transducin (T) to choleratoxin (CT) in retinal cells depends on illumination and on the presence of GTP or analogs. Low concentrations of GPP‐NH‐P or GPP‐CH 2 ‐P increase ADP‐ribosylation while GTPγS inhibits it. We show that GTP analogs permanently activate an ADP‐ribosylating factor (ARF) which mediates CT action on retinal cell membranes: when transducin‐depleted membranes were pre‐activated by GTP analogs, re‐added transducin became sensitive to CT in the absence of nucleotide, and presence of photoexcited rhodopsin (R*). Any subsequent G‐nucleotide addition (even GDP) decreased ADP‐ribosylation. Thus nucleotide‐free transducin molecule in R*—T empty complex is the CT substrate.