Photopigment
Photopigments are unstable pigments that undergo a chemical change when they absorb light. The term is generally applied to the non-protein chromophore moiety of photosensitive chromoproteins, such as the pigments involved in photosynthesis and photoreception. In medical terminology, "photopigment" commonly refers to the photoreceptor proteins of the retina.
Photosynthetic pigments
s convert light into biochemical energy. Examples for photosynthetic pigments are chlorophyll, carotenoids and phycobilins. 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 a biological membrane or via excitation and transfer of electrons released by photolysis. In chloroplasts, the light-driven electron transfer chain in turn drives the pumping of protons across the membrane.Photoreceptor pigments
The pigments in photoreceptor proteins either change their conformation or undergo photoreduction when they absorb a photon. This change in the conformation or redox state of the chromophore then affects the protein conformation or activity and triggers a signal transduction cascade.Examples of photoreceptor pigments include:
- retinal
- flavin
- bilin
Photopigments of the vertebrate retina