Kinetics of violaxanthin de-epoxidation by violaxanthin de-epoxidase, a xanthophyll cycle enzyme, is regulated by membrane fluidity in model lipid bilayers. Eur J Biochem

Department of Plant Physiology and Biochemistry, The Jan Zurzycki Institute of Molecular Biology and Biotechnology, Jagiellonian University, Kraków, Poland.
European Journal of Biochemistry (Impact Factor: 3.58). 10/2002; 269(18):4656-65. DOI: 10.1046/j.1432-1033.2002.03166.x
Source: PubMed


This paper describes violaxanthin de-epoxidation in model lipid bilayers. Unilamellar egg yolk phosphatidylcholine (PtdCho) vesicles supplemented with monogalactosyldiacylglycerol were found to be a suitable system for studying this reaction. Such a system resembles more the native thylakoid membrane and offers better possibilities for studying kinetics and factors controlling de-epoxidation of violaxanthin than a system composed only ofmonogalactosyldiacylglycerol and is commonly used in xanthophyll cycle studies. The activity of violaxanthin de-epoxidase (VDE) strongly depended on the ratio of monogalactosyldiacylglycerol to PtdCho in liposomes. The mathematical model of violaxanthin de-epoxidation was applied to calculate the probability of violaxanthin to zeaxanthin conversion at different phases of de-epoxidation reactions. Measurements of deepoxidation rate and EPR-spin label study at different temperatures revealed that dynamic properties of the membrane are important factors that might control conversion of violaxanthin to antheraxanthin. A model of the molecular mechanism of violaxanthin de-epoxidation where the reversed hexagonal structures (mainly created by monogalactosyldiacylglycerol) are assumed to be required for violaxanthin conversion to zeaxanthin is proposed. The presence of monogalactosyldiacylglycerol reversed hexagonal phase was detected in the PtdCho/monogalactosyldiacylglycerol liposomes membrane by 31P-NMR studies. The availability of violaxanthin for de-epoxidation is a diffusion-dependent process controlled by membrane fluidity. The significance of the presented results for understanding themechanism of violaxanthin de-epoxidation in native thylakoid membranes is discussed.

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Available from: Kazimierz Strzalka, Mar 10, 2015
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    • "Role of MGDG in V de-epoxidation. The presence of the main thylakoid membrane lipid monogalactosyldiacylglycerole (MGDG) is essential for the efficient de-epoxidation of V to A and Z (Fig. 2, Latowski et al., 2002; Goss et al., 2005, 2007). The role of MGDG is twofold: first, it serves as solubilizing agent for the hydrophobic xanthophyll cycle pigment V, thus making the substrate accessible for the enzyme VDE (Goss et al., 2005). "
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    • "A high concentration of Dt in the thylakoid lipid phase is in line with increased photoprotection by Dt (Lepetit et al. 2010). Additionally, MGDG forms what are termed inverted hexagonal (H II ) phases essential for efficient de-epoxidation (Latowski et al. 2002; Goss et al. 2005, 2007). H II phases are likely associated with the FCP complexes and represent the docking sites for DDE once the enzyme has been activated by ΔpH (Lepetit et al. 2010, 2012), i.e. the MGDG shield around the LHC targets DDE to the site where the majority of Dd is located. "
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    • "De-epoxydation was stopped by mixing 700 ml of assay mixture with 50 ml of 1 M KOH (Yamamoto, 1985). The level of xanthophyll pigments (violaxanthin as a substrate, antheraxanthin and zeaxanthin as products) was analyzed by reverse phase HPLC chromatography (Latowski et al., 2002). "
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