Structural studies on phycobiliproteins III. Comparison of bilin-containing peptides from the beta subunits of C-phycocyanin, R-phycocyanin, and phycoerythrocyanin.

Pure bilin-containing peptides were isolated from the /l subunits of Porphyridium aerugineum C-phycocyanin, Porphyridium cruentum R-phycocyanin, and Anabaena uariabilis phycoerythrocyanin after cleavage with cyanogen bromide.The /3 subunits of C-phycocyanin and phycoerythrocyanin each carry two phycocyanobilin prosthetic groups, while the j3 subunit of R-phycocyanin carries one phycocyanobilin and one phycoerythrobilin.Both bilin peptides were isolated from C-and R-phycocyanin, but only one was purified from phycoerythrocyanin.In each case, as found for Synechococcus sp.6301 C-phycocyanin (Williams, V. P., and Glazer, A. N. ( 1978) J. Biol.Chem.253, ZOZ-2111, one of the bilin peptides represented the COOH-terminal region of the /3 subunit.The sequences of the bilin peptides from the /3 subunit of Synechococcus sp.C-phycocyanin (I) are compared with those of P. aerugineum C-phycocyanin (II), R-phycocyanin (III), and phycoerythrocyanin (IV):