14N AND 15N COUPLING CONSTANTS OF THE OXIDIZED PRIMAR Y DONOR P-860 OF BACTERIAL PHOTO-IS OBTAINED BY ELECTRON SPIN ECHCI ENVELsOPE MODULATlON!SPECTROSCOPY

An electron spm echo modulation frequency analysis of P*-860 is performed in 14N chromatophores of RhodospiMhn ncbrum, and in “‘N substituted reaction centers from Rhodopseudomonas spheeroides 2.4.1, For the 14N matcnal two sets of nuclear quadrupole parameters are obtained. From the frequencies found for 15N reaction centers the perpendicular, paraIM and isotropic hypcrfime coupling constants of three of the four bactcriochlorophyll nitrogen nuclei are inferred. 1 _ In~duction In order to investrgate the structure of the primary donor P+-S60 in bacterial photosynthesis, electron-spin double and triple magnetic resonance techniques have been used, yleldmg information about the hyper-fine interactions [l-S] _ Another method to obtain information about, in particular, the weak electron-nuclear couplings of this radical, is frequency anal-ysis of the electron spin echo envelope modulation (ESEEM) [6,7] _ These couphngs, e g. of the nitrogens, may provide cntical data with respect to the specia