MAGNETIC CIRCULAR-DICHROISM INVESTIGATION ON CHROMOPHORES IN REACTIONCENTERS OF PHOTOSYSTEM-I AND PHOTOSYSTEM-II OF GREEN PLANT PHOTOSYNTHESIS

Magnetic circular dichorism (MCD) of chlorophylls (Chl) in P700-enrich ed (12 Chl/P700) photo-system (PS) I particles and D1-D2-cyt b559 (PSI I reaction center) particles isolated from spinach are measured in the wavelength region between 450 and 750 nm. The relative magnitude of M CD to absorption intensity ([MCD]/[Abs]) is found to be a good measure to estimate the interaction of chromophores (dimer or monomer). The d ifference spectrum between reduced and oxidized state for the 12 Chl/P 700 particles can be interpreted to be composed of a positive MCD from P700 and a negative MCD for P700+. MCD signals for the primary accept or Chl a monomer (A0) and the reduced cytochrome f are also observed. The MCD signal from pheophytin a in the PSII reaction center is remark ably in the Q(x) region as strong as the signal from the reaction cent er chlorophylls (P680 and accessory) and other attached chlorophylls. Based on the data, the MCD bands, as well as the absorption bands in t he Q(y) region, are deconvoluted into the contribution from reaction c enter chlorophylls and the other chlorophylls. The [MCD]/[Abs] ratio o f P680 or P700 is small and similar to that of special pair bacterioch lorophylls in the reaction center of purple bacteria, indicating the s pecific feature of MCD signals that originate from a dimer-type intera ction.