Movement of a sub-population of the light harvesting complex (LHCII) from grana to stroma lamellae as a consequence of its phosphorylation |
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Authors: | David J. Kyle Ting-Yun Kuang Janet L. Watson Charles J. Arntzen |
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Affiliation: | MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824 U.S.A. |
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Abstract: | Phosphorylation in vitro of the light-harvesting chlorophyll protein complex associated with Photosystem II (LHCII) resulted in the lateral migration of a subpopulation of LHCII from the grana to the stroma lamellae. This movement was characterized by a decrease in the chlorophyll ratio and an increase in the 77 K fluorescence emission at 681 nm in the stroma lamellae following phosphorylation. Polyacrylamide gel electrophoresis indicated that the principal phosphoproteins under these conditions were polypeptides of 26–27 kDa. These polypeptides increased in relative amount in the stroma lamellae and decreased in the grana during phosphorylation. Pulse/chase experiments confirmed that the polypeptides were labelled in the grana and moved to the stroma lamellae in the subsequent chase period. A fraction at the phospho-LHCII, however, was unable to move and remained associated with the grana fraction. LHCII which moved out into the stroma lamellae effectively sensitized Photosystem I (PS I), since the ability to excite fluorescence emission at 735 nm (at 77 K) by chlorophyll b was increased following phosphorylation. These data support the ‘mobile antenna’ hypothesis proposed by Kyle, Staehelin and Arntzen (Arch. Biochem. Biophys. (1983) 222, 527–541) which states that the alterations in the excitation-energy distribution induced by LHCII phosphorylation are, in part, due to the change in absorptive cross-section of PS II and PS I, resulting specifically from the movement of LHCII antennae chlorophylls from the PS-II-enriched grana to the PS-I-enriched stroma lamellae. |
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Keywords: | Light-harvesting complex Protein phosphorylation Excitation-energy distribution Chloroplast membrane (Pea thylakoid) Chl chlorophyll light-harvesting chlorophyll-protein complex of Photosystem II PS I Photosystem I PS I Photosystem II RC I reaction center of Photosystem I RC II reaction center polypeptides of Photosystem II |
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