Light activation of one rhodopsin molecule causes the phosphorylation of hundreds of others. A reaction observed in electropermeabilized frog rod outer segments exposed to dim illumination
- Univ. of Wisconsin, Madison (USA)
A rhodopsin phosphorylation reaction that occurs with high-gain is observed if measurements are made in electropermeabilized frog rod outer segments (ROS) stimulated by a dim flash of light in the operating range of the photoreceptor. Flashes of light exciting 1000 or fewer of the 3 x 10(9) rhodopsins present/ROS results in the incorporation of 1400 phosphates from ATP into the rhodopsin pool for each excited rhodopsin (Rho*). This amplification decreases with increasing light intensity, falling most sharply after each disk has absorbed one photon. The high-gain reaction is lost if the ROS are broken into vesicles by shearing, leaving a low-gain rhodopsin phosphorylation characterized in previous studies using brighter illumination. The high-gain but not the low-gain phosphorylation appears to be regulated by G-protein and by calcium levels in the range over which intracellular calcium changes when rod photoreceptors are illuminated. Kinetic measurements made on the phosphorylation observed at higher light intensities shows that it initially occurs rapidly enough for a role in terminating the photoresponse. The high-gain phosphorylation observed at lower light intensities may play a global role in regulating light-adaptation of the rod photoreceptor, and its existence suggests that a search for a similar high-gain modification in systems using the homologous beta-adrenergic or muscarinic acetylcholine receptors might be rewarding.
- OSTI ID:
- 6511411
- Journal Information:
- Journal of Biological Chemistry; (USA), Journal Name: Journal of Biological Chemistry; (USA) Vol. 265:25; ISSN 0021-9258; ISSN JBCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
ADP
ALKALINE EARTH METALS
AMINES
AMPHIBIANS
ANIMALS
AQUATIC ORGANISMS
AROMATICS
AZAARENES
BODY
BODY AREAS
CALCIUM
CHEMICAL REACTIONS
ELECTROMAGNETIC RADIATION
ELEMENTS
EYES
FACE
FROGS
GUANINE
HEAD
HETEROCYCLIC COMPOUNDS
HYDROXY COMPOUNDS
ISOTOPE APPLICATIONS
ISOTOPES
METALS
NUCLEOTIDES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANS
PHOSPHORUS ISOTOPES
PHOSPHORYLATION
PIGMENTS
PROTEINS
PURINES
RADIATIONS
RETINA
RHODOPSIN
SENSE ORGANS
TRACER TECHNIQUES
VERTEBRATES
VISIBLE RADIATION