Rhodopsin
Light-sensitive protein enabling dim-light vision in rod cells.
Rhodopsin, also known as visual purple, is a light-sensitive G-protein-coupled receptor (GPCR) encoded by the RHO gene. It is found in the outer segment discs of rod cells and mediates scotopic (dim light) vision, making it essential for night vision. Defects in the rhodopsin gene cause retinal diseases such as retinitis pigmentosa and congenital stationary night blindness.
- discovered_by
- Franz Christian Boll in 1876
- named_by
- Wilhelm Friedrich Kühne in 1878
- type
- G-protein-coupled receptor (GPCR)
- gene
- RHO
- function
- Triggers visual phototransduction in rod cells
- peak_absorption
- ~500 nm (green-blue light)
- associated_diseases
- Retinitis pigmentosa, congenital stationary night blindness
Lore & Background
Rhodopsin was discovered by Franz Christian Boll in 1876. The name derives from Ancient Greek ῥόδον (rhódon) for 'rose', due to its pinkish color, and ὄψις (ópsis) for 'sight', coined in 1878 by German physiologist Wilhelm Friedrich Kühne. The holoprotein nature of rhodopsin—composed of retinal and an apoprotein—was established by earlier researchers, who also introduced the term 'opsin'; George Wald later popularized the terms 'scotopsin' and 'photopsin' for the rod and cone apoproteins, respectively. Wald and colleagues also isolated iodopsin from chicken retinas, the first known cone opsin, naming its apoprotein photopsin and the rod apoprotein scotopsin.
Reader's Guide
Rhodopsin is a foundational molecule in vision science, as the first opsin whose amino acid sequence and 3D structure were determined (from cattle). Its mechanism—where 11-cis-retinal isomerizes to all-trans-retinal upon absorbing a photon—converts a chemoreceptor into a photoreceptor, initiating the phototransduction cascade via the G-protein transducin. This cascade leads to hyperpolarization of rod cells and changes in neurotransmitter release. Rhodopsin's high density in rod outer segment membranes facilitates photon capture but hinders G-protein diffusion. Mutations in the rhodopsin gene cause retinal diseases, including retinitis pigmentosa (often via constitutive activity or defective trafficking) and congenital stationary night blindness. The study of rhodopsin intermediates (e.g., bathorhodopsin, metarhodopsin II) has been central to understanding phototransduction and GPCR signaling.
Did You Know?
- Rhodopsin most strongly absorbs green-blue light (~500 nm) and appears reddish-purple, hence the archaic term 'visual purple'.
- When rhodopsin is exposed to light, it immediately photobleaches; full dark adaptation in humans takes 30–45 minutes, and complete regeneration may require longer depending on conditions.
- The retinal binding lysine (Lys296) is conserved in almost all opsins; opsins without it are not light sensitive.
- Rhodopsin was the first opsin whose amino acid sequence and 3D structure were determined, using cattle rhodopsin.
More in Sensory Systems 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record