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Phycocyanin Sensitizes both Photosystem I and Photosystem II in Cryptophyte Chroomonas CCMP270 Cells

Chantal D. van der Weij-De Wit ^*, Alexander B. Doust ^*, Ivo H. M. van Stokkum ^*, Jan P. Dekker ^*, Krystyna E. Wilk , Paul M. G. Curmi   and Rienk van Grondelle ^*

^* Department of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, 1081 HV Amsterdam; School of Physics and Centre for Immunology, The University of New South Wales, Sydney, N.S.W., Australia; and Centre for Immunology St. Vincent's Hospital, Sydney, N.S.W., Australia

Correspondence: Address reprint requests to Rienk van Grondelle, Tel.: 31-20-598-7930; Fax: 31-20-598-7999; E-mail: R.van.Grondelle{at}few.vu.nl.

This article presents an investigation of the energy migration dynamics in intact cells of the unicellular photosynthetic cryptophyte Chroomonas CCMP270 by steady-state and time-resolved fluorescence measurements. By kinetic modeling of the fluorescence data on chlorophyll and phycocyanin 645 excitation (at 400 and 582 nm respectively), it has been possible to show the excited state energy distribution in the photosynthetic antenna of this alga. Excitation energy from phycocyanin 645 is distributed nearly equally between photosystem I and photosystem II with very high efficiency on a 100-ps timescale. The excitation energy trapping times for both photosystem I (30 ps) and photosystem I (200 and 540 ps) correspond well to those obtained from experiments on isolated photosystems. The results are compared with previous results for another cryptophyte species, Rhodomonas CS24, and suggest a similar membrane organization for the cryptophytes with the phycobiliproteins tightly packed in the thylakoid lumen around the periphery of the photosystems.