Purification and characterization of phycocyanin from the marine cyanobacterium Synechococcus sp. IO9201

Abstract

This paper describes a suitable method for the optimum extraction and isolation of phycocyanin from the cyanobacterium Synechococcus sp. IO9201 isolated from Caribbean waters. Phycocyanin from this microorganism was purified to homogeneity and some of its properties were investigated. The purification steps consisted of extraction, hydrophobic interaction chromatography and ion exchange chromatography. Freezing at −21°C-thawing at 4°C, using an alkaline buffer was the best method for extracting phycocyanin from Synechococcus sp. IO9201. The best extraction was obtained using butyl-sepharose resin for hydrophobic interaction chromatography and 0.05 M Tris-HCl (pH = 7) containing 10% ethanol for phycocyanin elution. Finally, phycocyanin was further purified by ion exchange chromatography using Q-sepharose and eluted with a complex isocratic system. The estimated molecular weight of the phycocyanin purified from Synechococcus sp. IO9201 was 102 000 daltons by gel filtration and the isoelectric point was 4.6. When analyzed by SDS-PAGE, Synechococcus sp. IO9201 phycocyanin migrated as two bands having an apparent molecular weight of 21 360 and 18 980 Da. The first band corresponds to β phycocyanin subunits, whereas the second corresponds to α phycocyanin subunits. So, this phycocyanin was characterized as (αCPCβCPC)3.