Function of the photo-induced triplet radical pair in the photo-sensor BLUF protein

A photo-induced radical pair of FADH·and Y8·in BLUF protein SyPixD was studied by electron paramagnetic resonance(EPR)spectroscopy.The EPR signal has been characterized by a Pake doublet signal with complete S=1 spin state。The temperature dependence of the spin-lattice relaxation of the radical pair of flavin and tyrosine in SyPixD was investigated by pulsed electron paramagnetic resonance(EPR)spectroscopy.Based on the temperature dependence of spin.Lattice relaxation time T-1，the exchange coupling of the radical pair was estimated as2J=6to8厘米^&lt；-1&gt；，defined as-2JS-1*S-2.The radical pair was utilized as a probe to analyze the oligomer of SyPixD.The relative arrangement of PixD proteins in the complex was investigated by pulsed electron-electron double resonance(PELDOR)with the orientation selection。Based on the decameric structure in the crystal，the possible structure for the PELDOR results was evaluated.The transient EPR measurements have been performed to investigate the reaction pathway to produce radical-pair.The results show that the radical-pair was produced in the range of 200-263K.The possible reaction mechanism was proposed.

A photo-induced radical pair of FADH・and Y8・in BLUF protein SyPixD was studied by electron paramagnetic resonance(EPR) spectroscopy. The EPR signal has been characterized by a Pake doublet signal with complete S=1 spin state. The temperature dependence of the spin-lattice relaxation of the radical pair of flavin and tyrosine in SyPixD was investigated by pulsed electron paramagnetic resonance(EPR) spectroscopy. Based on the temperature dependence of spin. lattice relaxation time T-1, the exchange coupling of the radical pair was estimated as 2J=6 to 8 cm^<-1>, defined as-2JS-1* S-2.The radical pair was utilized as a probe to analyze the oligomer of SyPixD. The relative arrangement of PixD proteins in the complex was investigated by pulsed electron-electron double resonance(PELDOR) with the orientation selection. Based on the decameric structure in the crystal, the possible structure for the PELDOR results was evaluated.The transient EPR measurements have been performed to investigate the reaction pathway to produce radical-pair. The results show that the radical-pair was produced in the range of 200-263 K. The possible reaction mechanism was proposed.