Energy transfer between photosystem II units in a connected package model of the photochemical apparatus of photosynthesis.

A model of the photochemical apparatus of photosynthesis, presented previously in a tripartite format, is used in a bipartite format to analyze energy transfer between photosystem II units. The model is used to develop analytical expressions for the photochemical properties of chloroplasts that include a term for the probability for energy transfer between photosystem II units. In particular, a normalized plot of the fluorescence of variable yield as a function of the closure of photosystem II reaction centers permits the evaluation of the energy transfer parameter. Data from a study by Melis [Melis, A. (1978) FEBS Lett. 95, 202-206] are used to estimate that the probability for energy transfer between photosystem II units in the alpha component of photosystem II was approximately 0.57 when the photosystem II reaction centers were all open and 0.83 when the centers were closed. This connected package model appears to provide a better description of the system than the matrix model that was used previously.