opsin

opsin /op·sin/ (op´sin) a protein of the retinal rods (scotopsin) and cones (photopsin) that combines with 11-cis -retinal to form visual pigments.

---

op·sin (psn)

n.

A protein of the retina, especially the protein constituent of rhodopsin, that makes up one of the visual pigments.

---

opsin,

a protein that combines with retinal to form visual pigments (rhodopsin and iodopsin) in the photoreceptor cells of the retina.

---

opsin (op´sin),

n a visual pigment protein found in the retinal rods.

---

opsin

the protein component of retinal pigments, e.g. rhodopsin.

---

rhodopsin 

Visual pigment contained in the outer segments of the rod cells of the retina and involved in scotopic vision. When light stimulates the retina, the chromophore of the pigment molecule '11-cis' retinal (which is vitamin A aldehyde) isomerizes to 'all-trans' retinal. This leads to other chemical transformations which carry on even in the absence of light. The first stage is prelumirhodopsin, then lumirhodopsin and finally metarhodopsin (of which there are two types). This last transformation may lead to the breakdown of the molecule into retinal and opsin. The molecule is regenerated by recombining retinal and opsin with some enzymes. The absorption spectrum of rhodopsin has a maximum around 498 nm. The isomerization from '11-cis' to 'all-trans' also gives rise to the process of transduction in which the membrane potential covering the pigment molecules in the outer segment changes towards a hyperpolarization of the cell. This is the first step in the nervous response to a light stimulation of the retina. Syn. visual purple (not used any more); erythropsin. See dark adaptation; bleaching; receptor potential; absorption spectrum; transduction.