14N and 15N coupling constants of the oxidized primary donor P-860 of bacterial photosynthesis obtained by electron spin echo envelope modulation spectroscopy

An electron spin echo modulation frequency analysis of P ⁺-860 is performed in ¹⁴N chromatophores of Rhodospirillum rubrum, and in ¹⁵N substituted reaction centers from Rhodopseudomonas sphaeroides 2.4.1. For the ¹⁴N material two sets of nuclear quadrupole parameters are obtained. From the frequencies found for ¹⁵N reaction centers the perpendicular, parallel and isotropic hyperfine coupling constants of three of the four bacteriochlorophyll nitrogen nuclei are inferred.