Light-sensitivity modulating protein in frog rods

Photochem Photobiol. 1992 Dec;56(6):1173-80. doi: 10.1111/j.1751-1097.1992.tb09742.x.


Cyclic GMP is the second messenger in the phototransduction mechanism in rod photoreceptors. 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. Ca2+ 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 Ca2+ concentration decrease. In the present work, we isolated a protein that binds to disk membranes at high Ca2+ concentrations. In the presence of this protein (a 26 kDa protein), PDE light sensitivity becomes high at high Ca2+ concentrations. The effect was observed at physiological ranges of Ca2+ 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3',5'-Cyclic-GMP Phosphodiesterases / metabolism
  • Animals
  • Antigens, Neoplasm / isolation & purification
  • Calcium / metabolism
  • Calcium-Binding Proteins / isolation & purification
  • Cyclic GMP / metabolism
  • Eye Proteins*
  • Hippocalcin
  • Lipoproteins*
  • Nerve Tissue Proteins*
  • Photochemistry
  • Photoreceptor Cells / metabolism*
  • Photoreceptor Cells / radiation effects
  • Proteins / isolation & purification
  • Proteins / metabolism*
  • Proteins / radiation effects
  • Rana catesbeiana
  • Recoverin


  • Antigens, Neoplasm
  • Calcium-Binding Proteins
  • Eye Proteins
  • Lipoproteins
  • Nerve Tissue Proteins
  • Proteins
  • Recoverin
  • Hippocalcin
  • 3',5'-Cyclic-GMP Phosphodiesterases
  • Cyclic GMP
  • Calcium