[5] At the same time the protein was shown to be an effective quencher of singlet oxygen and was suggested to be involved in photoprotection, or carotenoid transport.

[6][7][8] In 2000, it was demonstrated that cyanobacteria could perform photoprotective fluorescence quenching independent of lipid phase transitions, differential transmembrane pH, and inhibitors.

[12] Photoactivation is accompanied by a pronounced color change, from orange to red, which had been previously observed by Kerfeld et al in the initial structural studies.

[7][8][5] In 2015 a combination of biophysical methods by researchers in Berkeley showed that the visible color change is the consequence of a 12Å translocation of the carotenoid.

[16] OCP is found in a majority of cyanobacterial genomes,[1][17] with remarkable conservation of its amino acid sequence, implying evolutionary constraints to preserve an important function.

[18] Under nutrient stress conditions, which are expected to be norm in marine environments, photoprotective mechanisms such as OCP become important even at lower irradiances.

[12][15] As evidenced by a decreased fluorescence, OCP in its red form is capable of dissipating absorbed light energy from the phycobilisome antenna complex.

[21][23][24] The temperature dependence of the rate of fluorescence quenching is similar to that of soluble protein folding,[25] supporting the hypothesis that OCPO slightly unfolds when it converts to OCPR.

In 2013 Kerfeld and co-workers showed that the NTD is the effector (quencher) domain of the protein while the CTD plays a regulatory role.

The activated OCPR form binds to allophycocyanin in the core of the phycobilisome and initiates the OCP-dependent photoprotective quenching mechanism.

Because of its high efficiency of fluorescence quenching, coupled to its low quantum yield of photoactivation by specific wavelengths of light, OCP has ideal properties as a photoswitch and has been proposed as a novel system for developing optogenetics technologies [1] and may have other applications in optofluidics and biophotonics.