C-phycocyanin (C-PC) from heterotrophic Galdieria sulphuraria. a G. sulphuraria grown in darkness on solid medium with glucose as carbon source. Clonal variants isolated from most intensively coloured colonies maintain high C-PC contents also in liquid cultures. Inset shows fluorescent micrograph of single heterotrophic G. sulphuraria cell with pigments stored in a characteristic u-shaped chloroplast. b Absorbance and fluorescence emission spectra of G. sulphuraria C-PC purified by (NH4)2SO4 fractionation. Inset (left) shows SDS-PAGE analysis of crude cell extract (C), and precipitates by 30% and 40% (NH4)2SO4 saturation, respectively, containing predominantly the α- and β-subunits of APC, and the α- and β- subunits of C-PC (A620/A280=2.7, food grade). Inset (right) C-PC extracts (240 mg L−1 ) photographed under white light (C-PC produces the blue colour) and UV light (C-PC fluoresces red). c Fluorescence intensities from tryptophan residues and phycocyanobilin in C-PC at increasing temperature. At approximately 60°C, C-PC denatures, seen as the abrupt decrease in tryptophan fluorescence, and phycocyanobilin fluorescence is lost. d Total and specific fluorescence intensities of C-PC at 642 nm as function of αβ monomer concentration. The relatively low specific fluorescence (total fluorescence divided by CPC concentration) below 0.1 μM is from αβ monomers. Above 0.3 μM, C-PC aggregates into α3β3 trimers and possibly α6β6 hexamers, and specific fluorescence is maximal. At higher C-PC concentrations, the linearity of the assay is lost. Inset shows specific fluorescence intensities at low C-PC concentrations at expanded scale. Data from Graverholt