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LIGHT‐SENSITIVITY MODULATING PROTEIN IN FROG RODS
Author(s) -
Kawamura Satoru
Publication year - 1992
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1992.tb09742.x
Subject(s) - rod , sensitivity (control systems) , biophysics , chemistry , biology , medicine , engineering , alternative medicine , pathology , electronic engineering
— Cyclic GMP is the second messenger in the phototransduction mechanism in rod photo‐receptors. Light‐induced activation of cGMP phosphodiesterase (PDE), the hydrolyzing enzyme of cGMP, reduces cytoplasmic cGMP concentration to close the cGMP‐activated channel and thereby causes a hyperpolarizing light response. Ca 2+ concentration decreases during light‐adaptation and this decrease is thought to be at least one of the underlying mechanisms of light‐adaptation. Our previous electrophysiological work suggested that PDE in frog rod photoreceptors is regulated by this Ca 2 + concentration decrease. In the present work, we isolated a protein that binds to disk membranes at high Ca 2+ concentrations. In the presence of this protein (a 26 kDa protein), PDE light sensitivity becomes high at high Ca 2+ concentrations. The effect was observed at physiological ranges of Ca 2+ concentrations. Thus we could explain high light‐sensitivity of photoreceptors under the dark‐adapted condition. According to its function, we termed the 26 kDa protein ‘sensitivity‐modulating protein’ or ‘S‐modulin’. During the purification we noticed that there are additional mechanisms present that may contribute to light‐adaptation in frog rod photoreceptors.