PHYCOERYTHROCYANIN: ITS SPECTROSCOPIC BEHAVIOR AND PROPERTIES

Abstract— Phycoerythrocyanin is a biliprotein found in very few blue-green algae. Its properties have been examined under three conditions: in whole cells, in light-harvesting organelles (the phycobilisomes). and as an isolated protein. Absorption and fluorescence bands characteristic of the isolated protein are essentially the same as those in intact cells of the blue-green alga Anabaena variabilis. The same spectroscopic hallmarks are observed in purified phycobilisomes. Dissociation of these physobilisomes at low-phosphate concentrations resulted in increased phycoerythrocyanin fluorescence. This time-dependent increase in fluorescence demonstrates the function of this biliprotein in excitation-energy transfer to the other biliproteins when the organelles are intact. The relative stabilities of the various heteroprotein bonds within the phycobilisomes are shown to possess differing phosphate ion dependencies. Studies on the isolated protein from Mastigocladus laminosus include fluorescence measurements at both 23 and-196°C, as is generally observed with biliproteins, although phycoerythrocyanin has complex visible absorption and excitation spectra, only a single emission band is observed.     

SELECTIVE ALTERATION OF THE PIGMENT COMPOSITION OF THE BLUE-GREEN ALGA, Anacystis nidulans

Abstract— Conditions were established which allow selective alteration of the pigment composition of Anacystis cells. Nitrate-starvation at 28°C and 39°C resulted in the preponderance of chlorophyll a (Chi a ) and that of phycocyanin (PC). In the case of starvation at 39°C strong correlation was observed between the disappearance of Chi a absorption and the appearance of an absorption band at 750 nm (P750) as the starvation proceeded. During regeneration the starved cells lost their P750 content. We show that P750 is quantitatively accounted for in the form of Chi a aggregates.     

THE DEVELOPMENT OF EXCITON MIGRATION ROUTES FOR PHYCOCYANIN 645 AND ALLOPHYCOCYANIN

Abstract— The origin of the comparatively complex absorption spectrum of the cryptomonad biliprotein, phycocyanin 645 from Chroomonas species, has been investigated by deconvolution of its absorption and CD spectra together with fluorescence polarization studies. The visible absorption and CD spectra were each deconvoluted into four components, three pure Gaussian and one Gaussian-Lorentzian chimera. The difference spectrum between the visible absorption spectra of partially renatured and partially dissociated protein and the fluorescence polarization spectrum are compared to these deconvolutions. All results are consistent with a previous proposal that band splitting from a pair of strongly-coupled dipoles contributes to the absorption and CD spectra of this biliprotein. A model for the flow of exciton migration through this protein is presented that incorporates these data [together with appropriate literature reports]. This exciton migration model together with one for the biliprotein, allophycocyanin, includes both strong and very weak coupling of dipoles. This combination of mechanisms has salient influence on the visible absorption spectra and the routes of exciton migration characteristic of these two proteins.