SELECTIVE DISRUPTION OF ENERGY-FLOW FROM PHYCOBILISOMES TO PHOTOSYSTEM-I

Efficient production of ATP and NADPH by the 'light' reactions of oxyg en-evolving photosynthesis demands continuous adjustment of transfer o f absorbed light energy from antenna complexes to Photosystem I (PS I) and II (PS II) reaction center complexes in response to changes in li ght quality. Treatment of intact cyanobacterial cells with N-ethylmale imide appears to disrupt energy transfer from phycobilisomes to Photos ystem I (PS I). Energy transfer from phycobilisomes to Photosystem II (PS II) is unperturbed. Spectroscopic analysis indicates that the indi vidual complexes (phycobilisomes, PS II, PS I) remain functionally int act under these conditions. The results are consistent with the presen ce of connections between phycobiliproteins and both PS II and PS I, b ut they do not support the existence of direct contacts between the tw o photosystems.