Isolation and characterization of thermostable phycocyanin from Galdieria sulphuraria

Abstract

Phycocyanin is a highly valuable pigmented protein synthesized by several species of cyanobacteria and red alga. In this study we demonstrate the production of thermostable phycocyanin from the unicellular red alga Galdieria sulphuraria. Phycocyanin was extracted by repeated freeze-thaw cycles and purified in a two-step process using ammonium sulfate fractionation, at 25% and 50% concentrations. Purified phycocyanin exhibited maximum absorbance at 620 nm, and the purity ratio (A(620)/A(280)) was found to be greater than 4. The recovery efficiency of phycocyanin from the crude extract was above 80%. In total, approximately 19 milligram pure phycocyanin was obtained from 3 g of wet cell mass of Galdieria sp. Subunits alpha and beta of the protein were separated by SDS-PAGE and analyzed by MALDITOF mass spectrometry for identification, which confirmed that the isolated protein is phycocyanin. The molecular weight of alpha and beta subunits of phycocyanin was found to be 17.6 and 18.4 kDa, respectively.