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J. Biol. Chem., Vol. 279, Issue 26, 26823-26829, June 25, 2004

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De-epoxidation of Violaxanthin in Light-harvesting Complex I Proteins^*

Antje Wehner, Stefanie Storf, Peter Jahns¶, and Volkmar H. R. Schmid

From the Institut für Biochemie der Pflanzen, Heinrich Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany and the Institut für Allgemeine Botanik, Johannes Gutenberg-Universität Mainz, Müllerweg 6, D-55128 Mainz, Germany

The conversion of violaxanthin (Vx) to zeaxanthin (Zx) in the de-epoxidation reaction of the xanthophyll cycle plays an important role in the protection of chloroplasts against photooxidative damage. Vx is bound to the antenna proteins of both photosystems. In photosystem II, the formation of Zx is essential for the pH-dependent dissipation of excess light energy as heat. The function of Zx in photosystem I is still unclear. In this work we investigated the de-epoxidation characteristics of light-harvesting complex proteins of photosystem I (LHCI) under in vivo and in vitro conditions. Recombinant LHCI (Lhcal-4) proteins were reconstituted with Vx and lutein, and the convertibility of Vx was studied in an in vitro assay using partially purified Vx de-epoxidase isolated from spinach thylakoids. All four LHCI proteins exhibited unique de-epoxidation characteristics. An almost complete Vx conversion to Zx was observed only in Lhca3, whereas Zx formation in the other LHCI proteins decreased in the order Lhca4 > Lhca1 > Lhca2. Most likely, these differences in Vx de-epoxidation were related to the different accessibility of the respective carotenoid binding sites in the distinct antenna proteins. The results indicate that Vx bound to site V1 and N1 is easily accessible for de-epoxidation, whereas Vx bound to L2 is only partially and/or with the slower kinetics convertible to Zx. The de-epoxidation properties determined for the monomeric recombinant proteins were consistent with those obtained for isolated native LHCI-730 and LHCI-680 in the same in vitro assay and the de-epoxidation state found under in vivo conditions in native LHCIs.

Received for publication, March 3, 2004 , and in revised form, March 30, 2004.

^* This work was supported by Deutsche Forschungsgemeinschaft Grants Ja 665/2-2 (to P. J.) and Schm 1203/2-4 (to V. H. R. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

^¶ To whom correspondence should be addressed. Tel.: 49-211-81-13862; Fax: 49-211-81-13706; E-mail: pjahns{at}uni-duesseldorf.de.

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