Polypeptide γ-subunits of R-phycoerythrin

R-Phycoerythrin was purified from two species of red algae: Callithamnion corymbosum from the Black Sea and Antithamnion sparsum from the Sea of Japan. Three polypeptide γ-subunits differing slightly in molecular weight (31.6, 30.8 and 29.0 kDa) in a 1:5:2 stoichiometry were found in R-phycoerythrin from C. corymbosum by reverse-phase chromatography on a fast performance liquid chromatography (FPLC) system. The ratio of the total number of γ 1-, γ 2- and γ 3-subunits to the total number of α- and β-subunits of R-phycoerythrin was 1:12 and suggested the well-known (αβ) 6γ molecular structure. The chromophore contents of the γ-subunits were identical: three phycourobilins and two phycoerythrobilins. R-Phycoerythrin from A. sparsum also contained three γ-subunits but with different chromophore compositions: one carried three phycourobilins and two phycoerythrobilins while the other carried four phycourobilins and one phycoerythrobilin. The chromophore composition of the third γ-subunit remained unclarified.