S-modulin.
S-Modulin is a Ca2+-binding protein found in frog rod photoreceptors (1,2) and its bovine homologue is known as recoverin (3,4). In the Ca2+-bound form, S-modulin inhibits rhodopsin phosphorylation5 through inhibition of rhodopsin kinase. (6-9) Because rhodopsin phosphorylation is the quench mechanism of light-activated rhodopsin (R*), (10,11) the inhibition of the phosphorylation by S-modulin probably contributes to increase the lifetime of R* to result in sustained hydrolysis of cGMP5. The Ca2+ concentration decreases in the light in vertebrate photoreceptors, (12-14) and this decrease is essential for light-adaptation. (15,16) Thus, S-modulin is expected to regulate the lifetime of R* and thereby regulate the extent and the time course of hydrolysis of cGMP depending on the intensity of background light. With this mechanism, S-modulin is believed to regulate the waveform of a photoresponse and the efficiency of the light in the generation of a photoresponse.
Kawamura
Satoru
S
Department of Biology, Graduate School of Science, Osaka University, Machikane-yama 1-1, Toyonaka, Osaka 560-0043, Japan.
Tachibanaki
Shuji
S
D000818:Animals; D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D004594:Electrophysiology; D005136:Eye Proteins; D051597:Hippocalcin; D007150:Immunohistochemistry; D008027:Light; D008074:Lipoproteins; D008958:Models, Molecular; D009419:Nerve Tissue Proteins; D010766:Phosphorylation; D051603:Recoverin; D012243:Rhodopsin / Q000037:antagonists & inhibitors; D015398:Signal Transduction
D002135:Calcium-Binding Proteins; D005136:Eye Proteins; D008074:Lipoproteins; D009419:Nerve Tissue Proteins; D051603:Recoverin; D051597:Hippocalcin; D012243:Rhodopsin