[Molecular organization and pigment composition of R-phycoerythrin from the red alga Callithamnion rubosum]

p3phycoerythrin is the major phycobiliprotein of Rhodophyta and endows these algae with the characteristic color. R-phycoerythrin purified from red alga Calithamnion rubosom is composed of four dissimilar polypeptide subunits, alpha, beta, gamma, and delta. In calibrated SDS gel electrophoresis their molecular weights are 21 000, 21 600, 31 000 and 33 000 daltons, respectively. The stoichiometry of the subunits in the native protein is 9 alpha: 9 beta: 2 gamma: 1 delta. R-phycoerythrin carries two covalently linked apoprotein red tetrapyrrol pigments: phycoerythrobilin (PEB) and phycourobilin (PUB). Chemical and spectroscopic data show that alpha subunit carries solely two PEB chromophores, beta subunit--3 PEB and 1 PUB groups, gamma subunit--3 PEB and 2 PUB groups and delta subunit--1 or 2 PEB and 1 PUB groups. The chromophore and polypeptide structure of R-phycoerythrin is mostly composed of all known phycobiliproteins of red and blue-green algae.