Аннотация:Phycobilisomes (PBs) are water soluble megadalton light-harvest-ing complexes of cyanobacteria and red algae. They consist ofhundreds of phycobiliproteins containing thousands of bilin pig-ments, which are organized in an “energy funnel” to effectivelydeliver excitation to photosystems. Quenching of excess excita-tion energy is necessary for the photoprotection of light-harvest-ing complexes. In cyanobacteria quenching of PBs excitation isinduced by the orange carotenoid protein (OCP) which photoac-tivation occurs under high light conditions. However, recentstudies have shown that PBs can switch among various statesdepending on lighting conditions without OCP, presumably dueto intramolecular charge-transfer within a phycobilins, whichmight play an essential physiological role. In this work usingtime-resolved fluorescence spectroscopy with picosecond time res-olution in single photon counting mode we investigate spectro-scopic signatures of Synechocystis sp. PBs and their componentsin absence and in presence of activated OCP. Since PBs is a mul-tilevel system with energy transfer, we decided to use low energyquanta to excite the lowest energy levels of pigments in PBs core.Analysis of anti-Stokes fluorescence showed that the maximumfluorescence intensity of PBs is shifted to longer wavelengths byabout 30 nm compared to excitation to the absorption maximumof phycocyanin. These long-wavelength excited states are charac-terized by approximately 2 ns lifetime, which does not changewhen the OCP complex with the PBs is formed. We assume thatinvestigation of the nature of excited states, selectively excited inthe infrared region, can provide a better understanding of theprocesses of energy conversion in light-harvesting complexes andthe mechanisms of photoprotective reactions. This study wassupported by Russian Science Foundation (grant no. 21-44-00005).