text: OCP was first described in 1981 by Holt and Krogmann who isolated it from the unicellular cyanobacterium Arthrospira maxima, although its function would remain obscure until 2006.  The crystal structure of the OCP was reported in 2003. 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. In 2000, it was demonstrated that cyanobacteria could perform photoprotective fluorescence quenching independent of lipid phase transitions, differential transmembrane pH, and inhibitors.  The action spectrum for this quenching process suggested the involvement of carotenoids, and the specific involvement of the OCP was later demonstrated by Kirilovsky and coworkers in 2006.  In 2008, OCP was shown to require photoactivation by strong blue-green light for its photoprotective quenching function. 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. 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 [https://today.lbl.gov/2015/07/01/protein-shifts-more-than-just-color-for-cyanobacterial-photoprotection/ carotenoid].