title: Kinetics of violaxanthin de-epoxidation by violaxanthin de-epoxidase, a xanthophyll cycle enzyme, is regulated by membrane fluidity in model lipid bilayers.
abstract: 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.
authors.affiliation: Department of Plant Physiology and Biochemistry, The Jan Zurzycki Institute of Molecular Biology and Biotechnology, Jagiellonian University, Kraków, Poland.
authors.forename: Dariusz
authors.initials: D
authors.lastname: Latowski
authors.forename: Jerzy
authors.initials: J
authors.lastname: Kruk
authors.forename: Kvetoslava
authors.initials: K
authors.lastname: Burda
authors.forename: Marta
authors.initials: M
authors.lastname: Skrzynecka-Jaskier
authors.forename: Anna
authors.initials: A
authors.lastname: Kostecka-Gugała
authors.forename: Kazimierz
authors.initials: K
authors.lastname: Strzałka
mesh_terms: D038983:Galactolipids / Q000378:metabolism; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism; D000455:Medicago sativa; D008560:Membrane Fluidity; D008954:Models, Biological; D010088:Oxidoreductases / Q000378:metabolism*; D013696:Temperature; D014908:Triticum; D024341:Xanthophylls / Q000378:metabolism; D019207:beta Carotene / Q000031:analogs & derivatives* / Q000378:metabolism*
chemical_list: D038983:Galactolipids; D008051:Lipid Bilayers; D008081:Liposomes; D024341:Xanthophylls; C009909:monogalactosyldiacylglycerol; D019207:beta Carotene; C005613:violaxanthin; D010088:Oxidoreductases; C023290:violaxanthin de-epoxidase