Characterization of cryptomonad phycoerythrin and phycocyanin

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Phycoerythrin, a chromoprotein, from the cryptomonad alga Rhodomonas lens is composed of two pairs of nonidentical polypeptides ( α 2 β 2). This structure is indicated by a molecular weight of 54,300, calculated from osmotic pressure measurements and by sodium dodecyl sulfate (SDS) gel electrophoresis, which showed bands with molecular weights of 9800 and 17,700 in a 1:1 molar ratio. The s 20,w 0 of 4.3S is consistent with a protein of this molecular weight. Similar results were obtained with another cryptomonad phycoerythrin and a cryptomonad phycocyanin. Electrophoresis after partial cross-linking by dimethyl suberimidate revealed seven bands for the cryptomonad phycocyanin and six bands for cryptomonad phycoerythrin and confirmed the proposed structure. Spectroscopic studies on α and β subunits of cryptomonad phycocyanin and phycoerythrin were carried out on the separated bands in SDS gels. The individual polypeptides possessed a single absorption band with the following maxima: phycoerythrin ( R. lens), α at 565 nm, β at 531 nm; phycocyanin ( Chroomonas sp.), α at 644 nm, β at 566 nm. Fluorescence polarization was not constant across the visible absorption band regions of phycoerythrin ( R. lens and C. ovata) with higher polarizations located at higher wavelengths, as had also been previously shown for cryptomonad phycocyanin ( Chroomonas sp.). Combining the absorption spectra and the polarization results indicates that in each case the β subunit contains sensitizing chromophores and the α subunit fluorescing chromophores. The CD spectra of cryptomonad phycocyanin and both phycoerythrins were similar and were related to the spectra of the individual subunits. In Ouchterlony double-diffusion experiments the cryptomonad phycoerythrins and phycocyanins cross-reacted, with spurring, with phycoerythrin isolated from a red alga. The cryptomonad phycoerythrins were immunochemically very similar to each other and to cryptomonad phycocyanin, with little spurring detected.