Orientation of photosystem-I pigments. Investigation by low-temperature linear dichroism and polarized fluorescence emission |
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Authors: | P. Tapie Y. Choquet J. Breton P. Delepelaire F.-A. Wollman |
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Affiliation: | 1. Service de Biophysique, Dept. Biologie, CEN Saclay, 91191 Gif-sur-Yvette Cedex, France;2. Institut de Biologie Physico-chimique, rue P. et M. Curie, 75005 Paris France |
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Abstract: | Using absorption and fluorescence experiments at low temperature with polarized light on oriented samples, the orientation of PS-I-related pigments, both in green plants and in Chlamydomonas reinhardtii, has been investigated on isolated pigment-protein complexes and intact thylakoids. The following observations have been made. (i) The isolation procedure of PS I110, PS I65, LHC I and CP0) particles from pea and C. reinhardtii do not alter significantly the intrinsic orientation of the pigments inside the complexes; (ii) Chl b is a structural component of PS I, linked to the peripheral antenna, with an orientation with respect to the thylakoid plane different from that observed in the main light-harvesting complex (iii) PS I65 (i.e., ‘core’ PS I) of pea and C. reinhardtii contains identical chromophores having the same orientation with respect to the geometrical longest axis (axes) of the complexes. (iv) LHC I and CP0 (i.e., PS I ‘peripheral antenna’) of pea and C. reinhardtii have identical oriented chromophores, except that a long-wavelength component with a high anisotropy is only present in green plants. This set of pigments, which absorbs at 705–725 nm, has the same orientation as the dipoles emitting F735 and also as the QY transition of P-700. (v) All the long-wavelength fluorescence properties of the various studied membranes are explained by these data on isolated PS I complexes: wild-type C. reinhardtii and Chl-b-less barely fluoresce from the core pigments, while a CP1 deficient mutant of C. reinhardtii and wild-type barley fluoresce from the antenna pigments. |
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Keywords: | Photosystem I Linear dichroism Pigment orientation Chlorophyll-protein Polarized fluoresence emission (Pea, Barley, C reinhardtii) Chl chlorophyll LD linear dichroism PS I Photosystem I LHC light-harvesting complex |
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