The evolution of oxygenic photosynthesis, respiration and photoperception are connected with the appearance of cyanobacteria. The key compounds, which are involved in these processes, are tetrapyrroles: open chain — bilins and cyclic — chlorophylls and heme. The latter are characterized by their covalent bond with the apoprotein resulting in the formation of biliproteins. This type of photoreceptors is unique in that it can perform important and opposite functions—light‐harvesting in photosynthesis with the participation of phycobiliproteins and photoperception mediated by phycochromes and phytochromes. In this review, cyanobacterial phycobiliproteins and phytochrome Cph1 are considered from a comparative point of view. Structural features of these pigments, which provide their contrasting photophysical and photochemical characteristics, are analyzed. The determining factor in the case of energy migration with the participation of phycobiliproteins is blocking the torsional relaxations of the chromophore, its D‐ring, in the excited state and their freedom, in the case of phytochrome photoisomerization. From the energetics point of view, this distinction is preconditioned by the height of the activation barrier for the photoreaction and relaxation in the excited state, which depends on the degree of the chromophore fixation by its protein surroundings.
Cadmium sulfide nanoparticles (3.2 to 5.6 nm) are synthesized using R-phycoerythrin as a protein matrix. The effects of the reactant concentrations and solution pH on the particle size of CdS are examined. The optical and photochemical properties of the nanoparticles are studied. Selective fluorimetry results suggest that CdS particles ≥ 3.2 nm in diameter are heteroaggregates. It is found that, during photoreduction of methyl viologen dichloride, the synthesis of CdS nanoparticles resumes. The growth of CdS particles is presumably restricted by the dimensions of the channel in the center of the R-phycoerythrin hexamer (3.5 × 6 nm).
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