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A light‐stimulated increase of cyclic GMP in squid photoreceptors
Author(s) -
Saibil Helen R.
Publication year - 1984
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(84)80248-3
Subject(s) - rhodopsin , gtp' , squid , cyclic gmp , phosphodiesterase , visual phototransduction , biophysics , chemistry , guanylate cyclase , cyclic nucleotide , biochemistry , biology , nucleotide , receptor , enzyme , retinal , ecology , gene
Photoreceptor outer segments isolated from squid retina are known to contain a light‐activated GTP‐binding protein. Here it is shown that these photoreceptors contain around 0.01 mol cyclic GMP per mol rhodopsin. Adding GTP in the dark stimulates the production of 0.0003–0.001 mol cyclic GMP/mol rhodopsin per min. GTP and light cause a 2‐fold faster increase in cyclic GMP. These results show that either (1) squid rhodopsin activates a guanylate cyclase, or (2) there is a constant guanylate cyclase activity and photoexcited rhodopsin inhibits a cyclic GMP phosphodiesterase.