Is 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 '15 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 '15 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 '15 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 $\endgroup$ – aaaaaa May 4 '15 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. $\endgroup$ – WYSIWYG May 7 '15 at 6:48

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 '15 at 10:43
  • $\begingroup$ Absorption of light does not necessarily give rise to fluorescence, but may give rise to colour if the absorbed light is in the visible region, or to a characteristic absorption spectrum. Flavoproteins are yellow because they absorb light somewhere about 420nm. Fluorescence is the emission of light of a longer wavelength. NADH absorbs light at 340nm. It is also fluorescent, emitting light with a peak at 460nm when excited at 340nm. Phosphorescence is like fluorescence, but light emission persists after the exciting source has been removed. $\endgroup$ – user1136 May 5 '15 at 14:45
  • $\begingroup$ 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 $\endgroup$ – aaaaaa May 5 '15 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 $\endgroup$ – aaaaaa May 5 '15 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 '15 at 17:37

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