DESCRIPTION OF ENERGY MIGRATION AND TRAPPING IN PHOTOSYSTEM-I BY A MODEL WITH 2 DISTANCE SCALING PARAMETERS

The energy transfer and trapping kinetics in the core antenna of Photo system I are described in a new model in which the distance between th e core antenna chlorophylls and P700 is proposed to be considerably lo nger than the distance between the chlorophylls within the antenna. St ructurally, the model describes the Photosystem I core antenna as a re gular sphere around P700, while energetically it consists of three lev els representing the bulk antenna, P700 and the red-shifted antenna pi gments absorbing at longer wavelength than P700, respectively. It is s hown that the model explains experimental results obtained from the Ph otosystem I complex of the cyanobacterium Synechococcus sp. (A.R. Holz warth, G. Schatz, H Brock, and E. Bittersman (1993) Biophys. J. 64: 18 13-1826) quite well, and that no unrealistic charge separation rate an d organization of the long-wavelength pigments has to be assumed. We s uggest that excitation energy transfer and trapping in Photosystem I s hould be described as a 'transfer-to-the-trap'-limited process.