Interpretation of the nitrogen spin densities in the primary donor cation of photosynthetic reaction centers

Abstract

Electron spin echo modulation investigation of the primary donor cation radical (P865 .+) of photosynthetic reaction centers yields a different set of anisotropic 15N hyperfine coupling constants from the values previously reported by ENDOR measurements [(1985) Proc. Natl. Acad. Sci. USA 81, 7792-7796]. The spin densities on the nitrogens, as reflected by our anisotropic coupling constants, support the special pair model for the primary donor cation, whereas spin densities based on anisotropic 15N hyperfine coupling constants of ENDOR are incompatible with either a monomer or a dimer model.