ENDOR Studies of the Electronic Structure of P740⁺ and P700⁺

Abstract

ESR and ENDOR spectra of P740⁺ in photosystem I (PS I) of Acaryouchloris marina were studied. The ENDOR spectrum of P740⁺ that seems to be a special pair of chlorophyll (Chl)d was compared with those of P700⁺ that is a dimer of Chl a and Chla' in spinach PS I. EPR and proton ENDOR spectra of purified Chla⁺ and Chld⁺ were also investigated. The numbers of ENDOR separations in P700⁺ were absent in the P740⁺ signal. The difference can be ascribed to the different chemical structures of Chla and Chld; a formyl group in Chla is replaced by a vinyl group in Chld. Electronic structure of P740⁺ was discussed based on the results.