Studies on R-phycoerythrins from two Antarctic marine red algae and a mesophilic red alga

R-phycoerythrin was purified from two benthic red algae, Iridaea cordata an d Phyllophora antarctica, obtained growing at -2 degrees C under thick sea ice off the coast of Antarctica. For the I. cordata protein, the molecular mass was 245,000 Da, and its secondary structure was 60% alpha helix, 17% b eta sheet, 16% turn, and 7% other. The light-harvesting faculties of the I. cordata protein resembled those of R-phycoerythrins from mesophilic red al gae and were distinctive from the novel R-phycoerythrin from P. antarctica. Deconvolution of the visible absorption spectrum of R-phycoerythrin from I . cordata indicated a minimum of five component bands having maxima at 568, 558, 534, 496, and 481 nm. R-phycoerythrins from the mesophilic Porphyra t enera and psychrophilic Phyllophora antarctica had the same five bands. The protein from Phyllophora antarctica obtained its unique spectrum from a mo re intense component at 482 nm, and a less intense band at 533 nm. This cha nge was probably produced by a replacement of phycoerythrobilin by phycouro bilin. A temperature study of the circular dichroism CD was obtained for R- phycoerythrin from I. cordata from 4 to 80 degrees C. Laser time-resolved f luorescence studies on R-phycoerythrin showed bilin to bilin energy transfe r with a 60.2-ps lifetime, which should occur by the Forster resonance. The similarities in spectra between the proteins from I. cordata and Porphyra tenera and the different spectrum for the protein from Phyllophora a antarc tica show that only particular antarctic habitats require unique R-phycoery thrins.