Talk:Rhodopsin

Hi, This is a good start on the rhodopsin page. Someone needs to expand it a bit (i.e. add 11-cis in front of the first retinaldehyde and add all-trans in front of the second. More important, rhodopsin absorbs green light (500 nm) not purple. Purple is not even a color of light. It results from the eye simultaneously registering red and blue light, which is what you get when you remove the green light from the mixture of colored light we call white. Rhodopsin looks purple because it absorbs green. It would also be good to add that there are lots of invertebrate rhodopsins besides the vertebrate ones. Otherwise, my 25 years of research experience with rhodopsin says you have done an excellent job. Best regards, James W. Lewis

I don't know why Emperorbma believed that rhodopsin absorbed the most at purple. If I understand the descriptions right, rhodopsin is really crimson (purplish-red), which makes sense since its peak absorbance is at a hue I call algæ (green-cyan), at 498 nm. Why can't I find a photograph of rhodopsin? lysdexia 01:55, 23 Nov 2004 (UTC)

All-trans retinal or a11-trans retinal

"light = 11-cis-retinal -> a11-trans-retinal -> conformational change in rhodopsin -> activate transducin (G protein) -> activate cGMP-phosphodiesterase -> cGMP hydrolyzes -> levels reduced in outer segment -> cGMP-sensitive Na+/Ca2+ channels in PM close -> PM hyperpolarized -> glutamate release inhibited = ø rod cell neurotransmitter released -> detected by bipolar cells -> stimulate ganglion cells -> transmit signal to brain"

Links

Online vitamins guide [1] was moved to vitamins article. Biophys 03:32, 14 November 2006 (UTC)

Merging?

This article should be merged with opsin. Any thoughts? Biophys 19:42, 5 September 2007 (UTC)

I'd recommend against the merge. The relationships among the opsins are complex, and can be better explained with separate articles. --Arcadian 22:29, 5 September 2007 (UTC)

I agree as long as Rhodopsin and photopsins (for example) are separate articles, as it is right now. If we had an article about rhodopsins as a family that includes photopsins, then a merging could be considered, since both articles would represent the same proteins, but only with and without retinal... Right now the system of articles about these proteins seems to be rather complicated, but I do not have a clear idea how to improve this. Biophys 00:40, 10 September 2007 (UTC)

Overcompentence?

I think metazoan might not be "good style". Most readers will need to follow the link in "is expressed in metazoan photoreceptor cell" to learn that it is animal. So please don't be so sharp that others bleed. 91.152.95.139 (talk) 08:54, 8 May 2008 (UTC)

I agree though I wouldn't call the practice of using unnecessary jargon at all competent. 'Metazoa' is best reserved for when a distinction has to be made with Protozoa. When the comparison is with bacteria, 'animals' will do. --Bendž|Ť 11:03, 8 May 2008 (UTC)

Intro sentence

Rhodopsin [...] is responsible for [...] the formation of the photoreceptor cells

Really? I would have guessed that the photoreceptor cells are responsible for the formation of rhodopsin. How does rhodopsin cause the photoreceptors to spring into existence? AxelBoldt (talk) 03:30, 10 March 2009 (UTC)

Picture on the right of the page

Hi everybody! Why is there picture of SRII, which is of course retinal-bound seven-helical transmembrane protein, but it is bacterial and not GPCR? --VGmonster (talk) 13:51, 16 June 2009 (UTC)

Removing the "Bleaching" section due to numerous errors and paucity of relevant information

The current version of the "Bleaching" section contains no relevant information and consists almost exclusively of factual errors. Just a few examples:

1. The section seems to attribute light adaption to the photobleaching of rhodopsin. Light adaptation has multiple components in photoreceptors involving the rates of cGMP hydrolysis by the phosphodiesterase, phosphorylation of rhodopsin, binding to arrestin, and the regulation of the guanylyl cyclase by intracellular calcium, etc, but depletion of rhodopsin is not one of them.
2. The section refers to "the threshold". What threshold? Rhodopsin is activated by a single photon of light. Photon absorption is a quantum event lacking a threshold. If the section refers to psychophysical experiments, then they have nothing to say about the photobleaching of rhodopsin.
3. The rest of the section describes an unrelated and unreferenced psychophysical experiment. The properties of photoreceptors and rhodopsin are measured more directly with single-cell recordings, patch clamp recordings, and other electrophysiological techniques.
4. What is "the vibrational energy derived from light"?
5. The section states that photoreceptors convert energy of light into electricity and pass it to bipolar cells. This description is inaccurate in several ways. First, photoreceptors form chemical synapses, not electrical synapses, with bipolar cells. Glutamate is used as the neurotransmitter. Photoreceptor cells do form electrical synapses between each other, but not with bipolar cells. Second, photoreceptors do not "convert" the energy of light into electricity. The energy of the phototransduction chain comes from metabolic processes. In fact, photoreceptor cells are hyperpolarized by light, which means that their membrane current decreases with light exposure (in vertebrates).
6. What does the electroretinogram tell us about the photobleaching of rhodopsin? The retina has multiple populations of cells with varying responses to light and no direct relationship to changes in the properties of rhodopsin can be elucidated from the ERG.

I am removing the entire section.

Yatsenko DV (talk) 01:03, 27 July 2009 (UTC)