Purification and characterization of the C-phycocyanin from Agmenellum quadruplicatum

The C-phycocyanin from the marine blue-green alga, Agmenellum quadruplicatum, has been isolated and purified to electrophoretic homogeneity. This is the first C-phycocyanin for which a low resolution three dimensional structure has been published (Hackert, M.L., Abad-Zapatero, C., Stevens, S.E. Jr. and Fox, J.L. (1977), J. Mol. Biol. 111, 365-369 and Abad-Zapatero, C., Fox, J.L. and Hackert, M.L. (1977) Biochem. Biophys. Res Commun. 78, 266-272). The native C-phycocyanin complex shows an absorption maximum at 622 nm and another peak at 355 nm. In urea solutions, the 622 nm maximum of whole C-phycocyanin is shifted to 662 nm. Am662 = 94400 was determined. The fluorescence emission maxima at 650 nm for haloprotein is shifted and largely quenched in acid urea. The monomeric protein consists of two polypeptide chains with molecular weights of 16,000 for the alpha chain and 18,500 for the beta chain. Spectra in 8 M urea indicate that the alpha chain possesses one and the beta chain two phycocyanobilin chromophores. The isolated chains show absorption maxima at 622 nm for the alpha chain and 608 nm for the beta chain. Amino acid compositions of the holoprotein and the separated chains are given and N-terminal amino acid sequences are presented.