Talk:Opsin

Merging?

This article should be merged with rhodopsin. Any thoughts? —Preceding unsigned comment added by Biophys (talk • contribs) 19:43, 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)

Perhaps you are right, I left my notice about merging in rhodopsin. I did not know about four photopsins in humans (one of them is not in SwissProt?).Biophys 00:53, 10 September 2007 (UTC)

Merging again?

Should we merge the opsin article with the retinylidene protein article? If not what is the difference between the two? --kupirijo (talk) 15:21, 5 May 2011 (UTC)

First sentence is not general enough

The first sentence of the article (Opsins are a group of light-sensitive 35-55 kDa membrane-bound G protein-coupled receptors of the retinylidene protein family found in photoreceptor cells of the retina) refers to the animal rhodopsin not a general opsin protein. --kupirijo (talk) 15:22, 5 May 2011 (UTC)

No plant opsins?

The article says, there are Type 1 and Type 2 opsins, present in animals and prokaryotes. What about microbial-type rhodopsins that are in plants (C. reinhardtii)? — Preceding unsigned comment added by 85.178.76.207 (talk) 19:49, 11 August 2011 (UTC)

C. reinhardtii isn't a plant, but it is a eukaryote. I haven't come across plants that have them yet, but this isn't my field;) A fungus has a type I proton-gradient forming opsin (http://www.pnas.org/content/102/19/6879.full) Pagelm (talk) 18:59, 26 February 2014 (UTC) (reply 31 Aug 2011)

Type I opsins

citation 5 does not really cover type I opsins (what little it does cite/address mainly concerns phototaxis in eukaryotic systems). Citation 10 within (Soppa, J. Two hypotheses—one answer. Sequence comparison does not support an evolutionary link between Halobacterial retinal proteins including bacteriorhodopsin and eukaryotic G protein-coupled receptors. FEBS Lett. 342, 7–11 (1994).) is probably a better source for type I to type II comparisons. Pagelm (talk) 18:59, 26 February 2014 (UTC) (orig. comment (31 Aug 2011)) - Edit: apologies for not spelling out sources, as numbers of citations in wiki are prone to change

Prokaryotic (type 1) opsins

The current evidence is inconclusive if the energy from Type I opsins can be used to fix CO2. All known archaea that have bacteriorhodopsin are photoheterotrophic (reliant on outside carbon sources). Bergey's says "CO2 fixation by halobacteria has been demonstrated on a number of occasions, but is believed to be due to several different anaplerotic mechanisms (danon and caplan 1977, javor 1988, rajagopalan and altekar 1991)." (perhaps not a direct quote). They went on to say something about RuBISCO being present, but at sub-relevant levels to cellular function (whatever that means) and referenced rajaopalan and altekar 1990. Around the time the 2001 edition of Bergey's came out, there was a 2000 paper from Beja's lab that said there MIGHT be autotrophy in the seas from proteorhodopsin, but later studies have shown there is a minimal increase in growth when light is around, and it doesn't seem to be autotrophic

Pagelm (talk) 18:38, 15 November 2011 (UTC)

Molecular Structure?

What I want to know is what these things are made of. Carbon? Hydrogen? Nitrogen? How many? This article is not complete until it includes that information. It is frustratingly difficult to find.75.129.91.157 (talk) 08:17, 7 December 2013 (UTC)

They are proteins, but the "business" of it is carried out by a bound carotenoid (or rather diterpene?) which is a hydrocarbon with some double bonds between the carbons to produce delocalized ("aromatic") electrons Pagelm (talk) 04:41, 15 February 2014 (UTC)

OPN1LW

In the section Animal (type 2) opsins subsection Vertebrate opsins is says, "Long Wavelength Sensitive (OPN1LW) Opsin – λmax in the red region of the electromagnetic spectrum. Despite its name, this receptor has a secondary response in the violet high frequencies." This is not correct. The peak sensitivity of the opsin is about 557-8, plus or minus a few nm due to normal genetic variation. Most people would perceive that wavelength as yellowish green. Then it gets scooted up a bit due to the yellow in the lens and the macular pigments, resulting in something more like greenish yellow. Red is perceived only when the L-cones receive at least five times as much stimulation as the M-cones, which happens at wavelengths above 610 nm.

I've fixed this, both in this page and in the OPS1LW page. Saying that the LWS's peak is in the red is a clear falsehood, it's a widespread misconception, and there's no reason to leave it in either page. I find that biology students perpetually get confused about this "because Wikipedia conflicts with my textbook" - time to fix this imho. I also added a sentence each page explicitly pointing out that "red opsin" is a misleading term. Sambakat (talk) 15:07, 8 February 2015 (UTC)

The alleged secondary peak is an artifact of normalization. Even though the S-cones are more sensitive than the L- and M-cones, there are far fewer of them. The human visual system has its own normalization mechanism, as so makers of graphs showing the LMS response curves. There are humps on the left side of all three cone sensitivity curves, but they merely approach horizontal for a while before continuing their descent. Zyxwv99 (talk) 03:05, 25 December 2014 (UTC)

I left this intact since I don't know about this "secondary peak". Should it just be deleted? Sambakat (talk) 15:07, 8 February 2015 (UTC)

I've been trying to find a reliable reference that explains the apparent secondary peak, but can't find one (even though I recall having read about this). Ideally it should be explained with an appropriate reference. The references we have now for this item (2 refs) are not reliable. For now, taking it out would probably be better, but I will keep looking. Zyxwv99 (talk) 15:09, 11 February 2015 (UTC)

By the way, the L-, M-, and S- cones are conventionally referred to as red-, green, and blue-cones, although this is considered informal usage. In research papers the formal and informal are often used interchangeably in the same paper. In works intended for the general public, clarification is necessary. This is actually a linguistic issue, like "positive" and "negative" electrical charge, named before the electron was discovered. A huge percentage of words in any language, including scientific terms, are like this. Zyxwv99 (talk) 15:14, 11 February 2015 (UTC)

Lead sentence needs revisiting

Given that "a great diversity of opsins can also be found in extraocular tissues"[[1]], doesn't our definition need rewording? DrChrissy ^(talk) 20:07, 1 May 2016 (UTC)

Sure, all human opsins are expressed in extraocular tissues. But then what else? One aspect is that the article is about the molecules that mediate vision, so that should be mentioned. Another thing is that the article also includes microbial opsins, even so their are not the main focus. So a proper definition would include them, too. So an opsin would be any receptor that detects light via a covalently bound retinal.

Another thing with the lead is that I have no idea what the five groups of opsins involved in vision are supposed to be. In human vision only, 4 kinds of opsins are involved, where the fifth one is - well, I don't know. Maybe it is referring to vertebrate vision, were we have LWS, SWS1, SWS2, RH1, and RH2, but that is still obscure.

And of course, vision does not mediate the conversion of a photon into a electrochemical signal. And that is not the first step of a phototransduction cascade, but the result of the phototransduction cascade.

Martin Gühmann (talk) 12:59, 18 May 2016 (UTC)