- A purplish-red thermolabile protein, MW about 40,000, found in the external segments of the rods of the retina; it is bleached by the action of light, which converts it to opsin and all-trans-retinal, and is restored in the dark by rhodogenesis; the dominant protein in the plasma membrane of rod cells. SYN: visual purple.- r. kinase an enzyme that regulates r. function by phosphorylating activated r. at a number of sites; phosphorylated photoactivated r. binds to arrestin.
* * *rho·dop·sin rō-'däp-sən n a red photosensitive pigment in the retinal rods of marine fishes and most higher vertebrates that is important in vision in dim light, is quickly bleached by light to a mixture of opsin and retinal, and is regenerated in the dark called also visual purple
* * *n.a pigment in the retina of the eye, within the rod, consisting of retinal - an aldehyde of retinol (vitamin A) - and a protein. The presence of rhodopsin is essential for vision in dim light. It is bleached in the presence of light and this stimulates nervous activity in the rods.
* * *rho·dop·sin (ro-dopґsin) [rhodo- + opsin] visual purple: a photosensitive purple-red chromoprotein in the retinal rods that is bleached and activated by light, producing stimulation of the retinal sensory endings as it is formed and degraded in the visual cycle (see illustration under cycle). It is a conjugated protein containing an 11-cis retinal prosthetic group linked to opsin.
Medical dictionary. 2011.