Extraction, purification and characterization of phycocyanin from Oscillatoria quadripunctulata—Isolated from the rocky shores of Bet-Dwarka, Gujarat, India

Phycocyanin is a major phycobiliprotein produced by cyanobacteria, but only few strains for its efficient purification have been reported until now. In the present study, we discussed the extraction, purification and characterization of C-phycocyanin from a novel isolate Oscillatoria quadripunctulata. The phycocyanin was extracted by repeated freeze–thaw cycles and purified by a three-step process: ammonium sulfate fractionation, Sephadex G-150 size exclusion chromatography and DEAE cellulose ion exchange chromatography. Purified phycocyanin showed absorbance maxima at 620 nm. A purity ratio (R) of 3.31 was achieved. The phycocyanin to phycoerythrin and phycocyanin to allophycocyanin ratio were 4.90 and 3.92, respectively. The recovery efficiency of C-phycocyanin from crude extract was above 68%. Twenty milligram pure phycocyanin was obtained from 10 g of dried cell mass. The purified protein showed pI of 5.0. The purity was checked by gel electrophoresis and UV-vis spectroscopy. High performance liquid chromatography (HPLC) determined the molecular weight of intact phycocyanin to be 215 kDa, whereas denaturing gel electrophoresis showed the presence of two bands of 19 and 20 kDa molecular mass, indicating the characteristic (αβ)6 subunit assembly of phycocyanin. Zinc-assisted fluorescence enhancement further confirmed that both subunits are bilin-linked polypeptides.