Abstract— C‐phycocyanin from Synechococcus sp. (Anacystis nidulans) shows photoreversible absorption changes when dissolved in buffer containing 75% ethylene glycol (vol/vol). Irradiation with red light (638 nm) causes a 7.5% decrease in absorbance around the absorption maximum (620 m), while the absorbance around 500 nm increases. Subsequent irradiation with green light (500 nm) partially reverses this change. Final photoreversibility at around 620 nm amounts to ca. 2.5% of the maximum absorbance. These reactions are ascribed to two interconvertible species PCr and PCg, the former with a higher absorbance in the red. the latter in the green. The rate of dark reversion from PCg to PCr is strongly enhanced by ferricyanide. It is proposed that with this reagent, dark reversion occurs via an oxidized form of PCg. Furthermore, ferricyanide in the presence of ethylene glycol is capable of reversibly oxidizing part of the chromophores of C‐phycocyanin, presumably to a radical. In the absence of ethylene glycol, however, ferricyanide causes total irreversible bleaching of the pigment in the dark. The induced photoreversibility of C‐phycocyanin is ascribed to the perturbing action on the protein structure by ethylene glycol in high concentrations. This solvent proved the most suitable perturbant of several compounds tested.
|Journal||Photochemistry and Photobiology|
|Publication status||Published - 1981|