Partially purified photosynthetic reaction centers from plant tissues.

The prior removal of carotenoids from photosynthetic membranes of plants by means of organic extraction allows Triton X-100 to remove and solubilize small particles that are greatly enriched in reaction center Chl, P700. Four plant species have been examined: spinach, bush bean (Phaseolus vulgaris), the blue-green alga Anabaena variabilis, and Euglena. The particles obtained are generally similar and have a ratio of one P700 to approximately 30 chlorophylls (in spinach the ratio is 1 to 28). Exposure of such particles to light or to ferrycyanide causes absorbance changes that are maximal in the vicinity of 700 and 680 nm. The former represents a bleaching (oxidation) of P700, and the latter appears to be caused by a red shift of some Chl closely associated with P700 in the reaction center. The kinetics of P700 oxidation and the fluorescent properties of such preparations indicate a decreased efficiency of energy transfer to the reaction center from the bulk Chl found on the particle.