Proton ENDOR study of the primary donor P740+, a special pair of chlorophyll d in photosystem I reaction center of Acaryochloris marina

Oxidized primary electron donor P740, a special pair of chlorophyll (Chl) d in photosystem (PS) I reaction center of a newly identified cyanobacterium Acaryochloris marina was studied by EPR and proton ENDOR spectroscopy. EPR and ENDOR spectra of P740+ were compared with those of P700+ in PS I reaction center of spinach. The g-factors of the purified Chl a+ and Chl d+ in CH2Cl2/THF, P700+ and P740+ in PS I reaction centers were determined to be 2.0025, 2.0032, 2.0027 and 2.0028, respectively. Hyperfine coupling constants of 1.9, 2.8 and 3.8 MHz that were detected in the ENDOR spectrum of P700+ were absent in the ENDOR spectrum of P740+. These features of P740+ were mainly ascribed to the difference between the chemical structures of Chl a and Chl d.