Isolation and Characterization of Water-Soluble Chromoproteins from Arthrospira platensis Cyanobacteria: C-Phycocyanin, Allophycocyanin, and Carotenoid- and Chlorophyll-Binding Proteins

Abstract

A method using chromatography on DEAE-Toyopearl 650M was developed for the simultaneous extraction of water-soluble chromoproteins from Arthrospira platensis cyanobacteria cells. These chromoproteins were C-phycocyanin, allophycocyanin, and carotenoid- and chlorophyll-binding proteins. The purity of the isolated C-phycocyanin was 4.42 (A₆₂₀/A₂₈₀). The allophycocyanin purity was 3.40 (A₆₅₂/A₂₈₀). The phycocyanin purity was confirmed by the presence of only two bands obtained during SDS-PAGE: α-subunit (17 kDa) and β-subunit (18 kDa). The isolated carotenoid- and chlorophyll-binding proteins were analyzed by high-performance exclusion chromatography on TSK-GEL 2000SW (XL) with detection at three wavelengths (280, 480, and 678 nm). The spectral, chromatographic, and electrophoretic analyses of chromoproteins, as well as pigment analysis, made it possible to conclude that the carotenoid—chlorophyll a binding protein was a xanthophyll-chlorophyll a protein complex, and the chlorophyll a binding protein was a chlorophyll a protein complex. The molecular weight of the proteins was determined by high-performance exclusion chromatography and SDS-PAGE to be 57 and 16 kDa, respectively. The photoprotective properties of these proteins and their possible functioning as part of evolutionary precursors of photosynthetic systems are discussed.