- Photopigment
Photopigments are unstable pigments that undergo a chemical change. The term is generally applied to the non-protein
chromophore moiety of photosensitivechromoprotein s, such as the pigments involved inphotosynthesis andphotoreception . In medical terminology, "photopigment" commonly refers to thephotoreceptor protein s of theretina .Photosynthetic pigments
Photosynthetic pigment (converting light into biochemical energy). Examples for photosynthetic pigments arechlorophyll ,carotenoid s andphycobilin s. These pigments enter a high-energy state upon absorbing a photon which they can release in the form of chemical energy. This can occur via light-driven pumping of ions across abiological membrane (e.g. in the case of the proton pumpbacteriorhodopsin ) or via excitation and transfer of electrons released byphotolysis (e.g. in thephotosystem s of thethylakoid membrane s of plantchloroplast s). Inchloroplast s, the light-driven electron transfer chain in turn drives the pumping of protons across the membrane.Photoreceptor pigments
The pigments in
photoreceptor protein s either change their conformation or undergophotoreduction when they absorb a photon. This change in the conformation orredox state of the chromophore then affects the protein conformation or activity and triggers asignal transduction cascade. Examples for photoreceptor pigments includeretinal (for example inrhodopsin ),flavin (for example incryptochrome ), and bilin (for example inphytochrome ).Photopigments of the vertebrate retina
In medical terminology, the term photopigment is applied to
opsin -type photoreceptor proteins, specificallyrhodopsin andphotopsin s, the photoreceptor proteins in the retinal rods and cones of vertebrates that are responsible forvisual perception , but alsomelanopsin and others.See also
*
Biological pigment
Wikimedia Foundation. 2010.