Magnetic field-induced fluorescence changes in chlorophyll-proteins enriched with P-700

Fluorescence yield dependence on external magnetic field (0-600 G) was measured for chlorophyll-protein complexes enriched with Photosystem I. Maximal relative changes of fluorescence yield at room temperature (1.0-2.5%) were dependent on the chlorphyll a:P-700 ratio. Magnetic field-induced changes were observed only in the presence of dithionite. At low temperatures (down to -160 degrees C) the magnetic field-induced effect decreased. The effect is obviously connected with the functions of reaction centers in Photosystem I. An explanation of the effect is proposed based on the hypothesis of radical pairs recombination within the reaction center. For the radical pair (P-700+. A-.), an intermediate acceptor, A-., with a g-value approximately equal to that of P-700+. is proposed.