Fractions enriched in Photosystem 1 or Photosystem 2 activity have been isolated from the cyanobacterium Chlorogloea fritschii after extraction of the membranes with digitonin and Triton X-100. Separation of the extract into the two components was achieved by using a Sepharose 6B column, calibration of which gave Kd values of 0.3 for the Photosystem 1 fraction and 0.53 for Photosystem 2. These values corresponded to molecular weights of approx. 500000 and 90000 respectively. The Photosystem 1 particle was shown to aggregate on storage and EDTA was shown to be necessary to separate the Photosystem 1 and 2 fractions.
