摘要: A new phycocyanin (PC) fluorescent subunit named β₂ (18 kDa) was isolated and characterized by both SDS-PAGE and isoelectric focusing (IEF) from a species of cryptophytic alga Chroomonas placoidea. PC was separated and purified by ammonium sulfate sedimentation followed by two steps of Sephadex G-100 chromatography. After denatured in 4 mol/L urea for 48 h, PC was divided into two fractions by passing through a Sephacryl S-100 chromatography column twice. The blue fraction (S-1) contained β subunits with a maximal absorbance at 595 nm in visible light region. While the green fraction (S-2) enriched in α subunits showed a characteristic long wavelength absorbance at 680-700 nm region and exhibited a relatively low molecular weight of 9.4 (α₁) and 8.5 kDa (α₂). Fraction S-1 also consisted of two different fluorescent subunits with molecular weight of 20.1 kDa (β₁) and 18 kDa (β₂) and differed from each other on isoelectric points of pH 5.7 (β₁) and 6.0 (β₂), respectively. Further investigation of peptide sequence will help a lot in elucidating the new subunit β₂ that was smaller in size and more neutral than the known β₁subunit, and may provide an alternative explanation in structure of cryptophytic phycobiliproteins.