C-phycocyanins, major biliproteins of blue green algae (cyanobacteria), widely used as colourants in food and
cosmetics are known for their
antioxidant as well as therapeutic potential. Recent claims indicating
phycobiliproteins exert stronger photodynamic action on
tumor cells than clinically approved
hematoporphyrin derivatives motivate us to investigate the photodynamic action of two newly isolated C-phycocyanins from Phormidium [PHR] and Lyngbya [LY] spp, respectively in comparison with known
C-phycocyanin from Spirulina sp. [SPI]. Photolysis of air saturated solutions of PHR, LY and SPI in the presence of 2,2,6,6-Tetramethyl piperidinol (TEMPL) generated three line EPR spectrum characteristic of 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxyl (
TEMPOL). The increase in intensity of the EPR spectrum with time of irradiation and decrease in intensity, in the presence of 1O2 quencher
DABCO confirm the formation of 1O2. Photoirradiation in the presence of spin trap
5,5-dimethyl-1-pyrroline-N-oxide (DMPO) generated EPR signal characteristic of O2(-) adduct. Efficiency of 1O2 generation is of the order LY > PHR> SPI. The yield of
reactive oxygen species (ROS) generation is found to be 1O2>O2(-) indicating type II mechanism to be the prominent pathway for photosensitation by phycocyanins.