Characterization of Phycocyanin from Chroomonas Species

Phycocyanin, a chromoprotein from Chroomonas sp., is characterized in regard to its size, subunit structure, amino acid composition, and spectroscopic properties. It is a monodisperse protein of 50,000 daltons and is composed of two polypeptide chains of 10,000 and two chains of 16,000 daltons. The proposed structure of the native protein is α2β2. The s020,w is 4.4 S, and the partial specific volume is 0.73. Unlike C-phycocyanin, a functionally related chromoprotein from blue-green and red algae, phycocyanin does not form a number of different aggregates. We suggest that the absence of these larger aggregates is related to its in vivo location. The amino acid composition of phycocyanin from Chroomonas sp. differs extensively from that of C-phycocyanin, with much greater amounts of serine, half-cystine, and lysine. Likewise, the circular dichroism and fluorescence spectra are very different, indicating major functional modifications.