A survey of marine unicellular cyanobacterial strains for phycobiliproteins with 
high phycourobilin (PUB) content led to a detailed investigation of 
Synechocystis sp. WH8501. The phycobiliproteins of this strain were purified and 
characterized with respect to their bilin composition and attachment sites. 
Amino-terminal sequences were determined for the alpha and beta subunits of the 
phycocyanin and the major and minor phycoerythrins. The amino acid sequences 
around the attachment sites of all bilin prosthetic groups of the phycocyanin 
and of the minor phycoerythrin were also determined. The phycocyanin from this 
strain carries a single PUB on the alpha subunit and two phycocyanobilins on the 
beta subunit. It is the only phycocyanin known to carry a PUB chromophore. The 
native protein, isolated in the (alpha beta)2 aggregation state, displays 
absorption maxima at 490 and 592 nm. Excitation at 470 nm, absorbed almost 
exclusively by PUB, leads to emission at 644 nm from phycocyanobilin. The major 
and minor phycoerythrins from strain WH8501 each carry five bilins per alpha 
beta unit, four PUBs and one phycoerythrobilin. Spectroscopic properties 
determine that the PUB groups function as energy donors to the sole 
phycoerythrobilin. Analysis of the bilin peptides unambiguously identifies the 
phycoerythrobilin at position beta-82 (residue numbering assigned by homology 
with B-phycoerythrin; Sidler, W., Kumpf, B., Suter, F., Klotz, A. V., Glazer, A. 
N., and Zuber, H. (1989) Biol. Chem. Hoppe-Seyler 370, 115-124) as the terminal 
energy acceptor in phycoerythrins.