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Abstract An in vitro analysis of the effects of photosynthetically active and ultraviolet radiations was executed to assess the photostability of biologically relevant pigments phycocyanin ( PC ), phycoerythrin ( PE ) and allophycocyanin ( APC ) isolated from Lyngbya sp. A09 DM . Ultraviolet ( UV ) irradiances significantly affected the integrity of PC , PE and APC ; however, PAR showed least effect. UV radiation affected the bilin chromophores covalently attached to phycobiliproteins ( PBP s). Almost complete elimination of the chromophore bands associated with α ‐ and β ‐subunit of PE and APC occurred after 4 h of UV ‐B exposure. After 5 h of UV ‐B exposure, the content of PC , PE and APC decreased by 51.65%, 96.8% and 96.53%, respectively. Contrary to PAR and UV ‐A radiation, a severe decrease in fluorescence of all PBP s was observed under UV ‐B irradiation. The fluorescence activity of extracted PBP was gradually inhibited immediately after 15–30 min of UV ‐B exposure. In comparison to the PC , the fluorescence properties of PE and APC were severely lost under UV ‐B radiation. Moreover, the present study indicates that UV ‐B radiation can damage the structural and functional integrity of phycobiliproteins leading to the loss of their ecological and biological functions. UV irradiances significantly affected the structural and functional integrity of biologically relevant molecules phycocyanin (PC, λmax: 615 nm), phycoerythrin (PE, λmax: 563 nm) and allophycocyanin (APC, λmax: 652 nm). UV radiation also affected the bilin chromophores covalently attached to phycobiliproteins (PBPs). The spectroscopic as well as sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) analyses of the PC, PE and APC of Lyngbya sp. showed a marked decrease in the PBPs content with an increase in UV exposure time. In comparison to the PC, the fluorescence properties of PE and APC were severely lost under UV‐B radiation.
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