Are there proteins that have strong color, that could be seen without the need of UV and with naked eyes (with white light) - in mammalian cells?

Searching for reporter, something like GFP, but that we could see it without UV (not fluorescence).

Like chromoprotein - but it is problematic in mammalian cells because most chromoproteins need a prosthetic group.

  • $\begingroup$ You've read the wikipedia page I assume? It has some examples. $\endgroup$
    – canadianer
    May 4, 2015 at 14:33
  • $\begingroup$ Yes. I searching for something that may be used like GFP (reporter), but that we could see it without fluorescence and it's not chromoprotein - because like I mention it not perfect in mammalian cells, as far as I know. $\endgroup$
    – Robertos
    May 4, 2015 at 14:43
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    $\begingroup$ The problem with these chromoproteins is that the color comes from a prosthetic group that is added to the protein later. If the cells can't produce the prosthetic group, or can't attach it to the protein, it won't be colored. I know you're not looking for fluorescent proteins, but I have seen E. coli express Red Fluorescent Protein and make reddish colonies, clearly visible on an agar gel. I can't say if mammalian cells would also make visibly red colonies. $\endgroup$
    – user137
    May 4, 2015 at 15:20
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    $\begingroup$ >"E. coli express Red Fluorescent Protein and make reddish colonies" Because they absorb almost all light from daylight (~white) spectrum $\endgroup$ May 4, 2015 at 18:32
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    $\begingroup$ @VGranin Many RFPs have their absorption maxima at around 500nm (green light) and therefore they can fluoresce even under white light. Since red scatters less it is easier to observe too. But the colouration is not very deep. So you can observe reddish colonies. $\endgroup$
    May 7, 2015 at 6:48

3 Answers 3


Have a look at this paper. They have isolated a chromoprotein similar to GFP, and like the latter it does not have any prosthetic group.

This protein — asFP595 (because it was isolated from the anemone Anemonia sulcata.), is purple coloured under white light and also exhibits a little fluorescent emission in the red region (λmax = 595 nm).

Also have a look at these two papers:


You are looking for light-emitting proteins. They gather energy from either absorption of photon (fluorescence) or via random thermal fluctuations. Problem is that fluorescence might be considered forced emission, whereas what you looking for is results of spontaneous transitions. That means that number of photons per second you can expect from latter proteins is $10^4$ times less (I don't have reference for that statement). You need very sensitive detectors and microscopy (sub- or just cellular) is almost impossible at that rate.

You should look into phosphorescence. Also, such thing as GFP-aeqorin might be of interest. That is a calcium-sensistive construct, might give you starting point in searching for reviews.

Another keyword is bioluminescence. See here for more: http://www.olympusconfocal.com/applications/fluorescentproteins.html

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    $\begingroup$ The question clearly specifies "that could be seen without fluorescence" $\endgroup$
    – nico
    May 5, 2015 at 10:43
  • $\begingroup$ phosphorescence is relaxation pathway from states with much longer life-time (ms versus ns for fluorescence). Fluorescence persists after "exciting source has been removed" too, relaxation is just much faster $\endgroup$ May 5, 2015 at 15:02
  • $\begingroup$ @nico Can you elaborate? My guess is that OP wants to see proteins without any harsh excitation light/in complete darkness, and I support OP in that endeavour $\endgroup$ May 5, 2015 at 15:03
  • $\begingroup$ @aandreev the OP says "something like GFP, but that we could see it without UV (not fluorescence)." so giving him information about GFP-related proteins does not really seem a good answer to me... My guess is he's after something like Bacteriorhodopsin which is purple (albeit I'm not sure it's a good idea to use it as a reporter...) $\endgroup$
    – nico
    May 5, 2015 at 17:37
  • $\begingroup$ @nico are you talking about GFP-aeqorin? it does not require any excitation, you can observe emitted light in complete darkness. Aeqorin is bioluminesce in presence of high Ca concentration, GFP is just a relay here. pnas.org/content/97/13/7260.fullhttp://www.pnas.org/content/97/… $\endgroup$ May 5, 2015 at 18:18

GFP-like non-fluorescent chromoproteins are colored and non-fluorescent. A handful of them - Rtms 5, HcRed, cgCP, gtCP and zFP538 - have reviewed pages on Uniprot. This paper from Nature describes the use of Rtms 5 to make hair dye: https://www.nature.com/articles/s41598-019-50283-0

  • $\begingroup$ Whilst true, it's not clear that this answers the question as written, which asks about non-fluorescent proteins found in human cells. Please take our tour and refer to the help center for guidance as to our ways. $\endgroup$ Feb 20, 2022 at 5:09

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