Characterization and antioxidant activity of selenium-containing phycocyanin isolated from Spirulina platensis

Selenium-containing phycocyanin (Se-PC) and its different aggregates - monomer (alpha beta), trimer (alpha beta)(3) and hexamer (alpha beta)(6), which are represented as Se-PC1, Se-PC2 and Se-PC3, as well as their alpha and beta subunits, were prepared and purified from selenium-rich Spirulina platensis. The Se speciation in Se-PC its aggregates and subunits, as well as the antioxidant activities of these compounds against free radicals of superoxide, hydrogen peroxide and 2,2-diphenyl-1-picryl-hydrazyl (DPPH.) were investigated. By gel filtration on SephadexG-200 column and SDS-PAGE, the molecular weight of Sc-PCl, 2, and 3 were determined to be 38.5, 116 and 247 kDa, respectively, and these of alpha and beta subunits were 17.8 and 19.5 kDa respectively. Se concentrations of Se-PCl, 2 and 3 were of 197, 289 and 422 mu g/g protein, respectively, and those of alpha and beta subunits were 126 and 187 mu g/g protein, respectively, which suggested that the Se content of Se-PC was decreased in the dissociation process of Se-PC and highly associated with its aggregation state. The antioxidant activities of Se-PC, its aggregates and subunits against different free radicals were found to be variable. Compared with phycocyanin without bound Se, although there were no differences among the DPPH.-scavenging activities of Se-PC, its a and P subunits and the pure phycocyanin, the superoxide and hydrogen peroxide radical-scavenging activities of Se-PC, as well as Se-PC2 and Se-PC3, were significantly higher and proved to be positively correlated with their Se contents. (c) 2005 Elsevier Ltd. All rights reserved.