The in vitro synergistic denaturation effect of heat and surfactant on photosystem I isolated from Arthrospira Platensis
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Photosystem I (PSI) generates the most negative redox potential found in nature, and the performance of solar energy conversion into alternative energy sources in artificial systems highly depends on the thermal stability of PSI. Thus, understanding thermal denaturation is an important prerequisite for the use of PSI at elevated temperatures. To assess the thermal stability of surfactant-solubilized PSI from cyanobacteria Arthrospira Platensis, the synergistic denaturation effect of heat and surfactant was studied. At room temperature, surfactant n-dodecyl-β-d-maltoside solubilized PSI trimer gradually disassembles into PSI monomers and free pigments over long time. In the solubilizing process of PSI particles, surfactant can uncouple pigments of PSI, and the high concentration of surfactant causes the pigment to uncouple more; after the surfactant-solubilizing process, the uncoupling is relatively slow. During the heating process, changes were monitored by transmittance T800nm, ellipticity θ686nm and θ222nm, upon slow heating (1.5 °C per minute) of samples in Tris buffer (20 mM, pH 7.8) from 20 to 95 °C. The thermal denaturation of surfactant-solubilized PSI is a much more complicated process, which includes the uncoupling of pigments by surfactants, the disappearance of surrounding surfactants, and the unfolding of PSI α-helices. During the heating process, the uncoupling chlorophyll a (Chla) and converted pheophytin (Pheo) can form excitons of Chla–Pheo. The secondary structure α-helix of PSI proteins is stable up to 87–92 °C in the low-concentration surfactant solubilized PSI, and high-concentration surfactant and pigments uncoupling can accelerate the α-helical unfolding.
KeywordsPhotosystem I Surfactant Solubilization Structural integrity Thermal stability
Critical micelle concentration
Dynamic light scattering
Transmittance at 800 nm
Ellipticity at 686 nm
Ellipticity at 222 nm
- A. platensis
Arthrospira platensis (old name: Spirulina platensis)
This work was financially supported by the National Natural Science Foundation of China (21673292), Shandong Provincial Natural Science Foundation (ZR2014BM013), and the Fundamental Research Funds for the Central Universities. The content is solely the responsibility of the authors and does not necessarily represent the official views of the supporters.
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Conflict of interest
The authors declare that they have no conflict of interest.
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