PHOTOACTIVE PHOTOSYSTEM-I PARTICLES WITH A MOLAR RATIO OF CHLOROPHYLL-A TO P700 OF 9

Lyophilized photosystem I particles from spinach were treated with diethyl ether that contained various organic solvents with different dielectric constants. More pigments were extracted as the dielectric constant of the solvent added to ether increased. The reaction-center chlorophyll-dimer, P700, was more resistant to extraction than the rest of the chlorophyll. Particles that contained only 6 chlorophylls in addition to P700 and the primary electron acceptor (A(0)), in a single reaction-center unit, were prepared by extraction with a mixture of ether and acetaldehyde. A distinct shoulder at 695 nm due to P700 or at 686 nm due to P700(+) was observed in the absorption spectra of the reduced or oxidized particles, respectively, even at room temperature. No secondary acceptor phylloquinone remained in the particles. Stable charge separation was restored upon the addition of 2-amino-anthraquinone, even though the particles had the lowest molar ratio of chlorophyll to P700 of any reported particles.