Publications

• Xanthophyll cycle enzymes are members of the lipocalin family, the first identified from plants.

  Bugos R.C., Hieber A.D., Yamamoto H.Y.

  Violaxanthin de-epoxidase and zeaxanthin epoxidase catalyze the addition and removal of epoxide groups in carotenoids of the xanthophyll cycle in plants. The xanthophyll cycle is implicated in protecting the photosynthetic apparatus from excessive light. Two new sequences for violaxanthin de-epoxi ... >> More

  Violaxanthin de-epoxidase and zeaxanthin epoxidase catalyze the addition and removal of epoxide groups in carotenoids of the xanthophyll cycle in plants. The xanthophyll cycle is implicated in protecting the photosynthetic apparatus from excessive light. Two new sequences for violaxanthin de-epoxidase from tobacco and Arabidopsis are described. Although the mature proteins are well conserved, the transit peptides of these proteins are divergent, in contrast to transit peptides from other proteins targeted to the thylakoid lumen. Sequence analyses of both violaxanthin de-epoxidase and zeaxanthin epoxidase establish the xanthophyll cycle enzymes as members of the lipocalin family of proteins. The lipocalin family is a diverse group of proteins that bind small hydrophobic (lipophilic) molecules and share a conserved tertiary structure of eight beta-strands forming a barrel configuration. This is the first reported identification of lipocalin proteins in plants. << Less

  J. Biol. Chem. 273:15321-15324(1998) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.

• The de-epoxidase and epoxidase reactions of Mantoniella squamata (Prasinophyceae) exhibit different substrate-specific reaction kinetics compared to spinach.

  Frommolt R., Goss R., Wilhelm C.

  In vivo the prasinophyceaen alga Mantoniella squamata Manton et Parke uses an incomplete violaxanthin (Vx) cycle, leading to a strong accumulation of antheraxanthin (Ax) under conditions of high light. Here, we show that this zeaxanthin (Zx)-depleted Vx/Ax cycle is caused by an extremely slow seco ... >> More

  In vivo the prasinophyceaen alga Mantoniella squamata Manton et Parke uses an incomplete violaxanthin (Vx) cycle, leading to a strong accumulation of antheraxanthin (Ax) under conditions of high light. Here, we show that this zeaxanthin (Zx)-depleted Vx/Ax cycle is caused by an extremely slow second de-epoxidation step from Ax to Zx, and a fast epoxidation from Ax back to Vx in the light. The rate constant of Ax epoxidation is 5 to 6 times higher than the rate constant of Zx formation, implying that Ax is efficiently converted back to Vx before it can be de-epoxidated to Zx. It is, however, only half the rate constant of the first de-epoxidation step from Vx to Ax, thus explaining the observed net accumulation of Ax during periods of strong illumination. When comparing the rate constant of the second de-epoxidation step in M. squamata with Zx formation in spinach (Spinacia oleracea L.) thylakoids, we find a 20-fold reduction in the reaction kinetics of the former. This extremely slow Ax de-epoxidation, which is also exhibited by the isolated Mantoniella violaxanthin de-epoxidase (VDE), is due to a reduced substrate affinity of M. squamata VDE for Ax compared with the VDE of higher plants. Mantoniella VDE, which has a similar Km value for Vx, shows a substantially increased Km for the substrate Ax in comparison with spinach VDE. Our results furthermore explain why Zx formation in Mantoniella cells can only be found at low pH values that represent the pH optimum of VDE. A pH of 5 blocks the epoxidation reaction and, consequently, leads to a slow but appreciable accumulation of Zx. << Less

  Planta 213:446-456(2001) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Plant lipocalins: violaxanthin de-epoxidase and zeaxanthin epoxidase.

  Hieber A.D., Bugos R.C., Yamamoto H.Y.

  Violaxanthin de-epoxidase and zeaxanthin epoxidase catalyze the interconversions between the carotenoids violaxanthin, antheraxanthin and zeaxanthin in plants. These interconversions form the violaxanthin or xanthophyll cycle that protects the photosynthetic system of plants against damage by exce ... >> More

  Violaxanthin de-epoxidase and zeaxanthin epoxidase catalyze the interconversions between the carotenoids violaxanthin, antheraxanthin and zeaxanthin in plants. These interconversions form the violaxanthin or xanthophyll cycle that protects the photosynthetic system of plants against damage by excess light. These enzymes are the first reported lipocalin proteins identified from plants and are only the second examples of lipocalin proteins with enzymatic activity. This review summarizes the discovery and characterization of these two unique lipocalin enzymes and examines the possibility of other potential plant lipocalin proteins. << Less

  Biochim Biophys Acta 1482:84-91(2000) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Abscisic acid biosynthesis in tomato: regulation of zeaxanthin epoxidase and 9-cis-epoxycarotenoid dioxygenase mRNAs by light/dark cycles, water stress and abscisic acid.

  Thompson A.J., Jackson A.C., Parker R.A., Morpeth D.R., Burbidge A., Taylor I.B.

  Two genes encoding enzymes in the abscisic acid (ABA) biosynthesis pathway, zeaxanthin epoxidase (ZEP) and 9-cis-epoxycarotenoid dioxygenase (NCED), have previously been cloned by transposon tagging in Nicotiana plumbaginifolia and maize respectively. We demonstrate that antisense down-regulation ... >> More

  Two genes encoding enzymes in the abscisic acid (ABA) biosynthesis pathway, zeaxanthin epoxidase (ZEP) and 9-cis-epoxycarotenoid dioxygenase (NCED), have previously been cloned by transposon tagging in Nicotiana plumbaginifolia and maize respectively. We demonstrate that antisense down-regulation of the tomato gene LeZEP1 causes accumulation of zeaxanthin in leaves, suggesting that this gene also encodes ZEP. LeNCED1 is known to encode NCED from characterization of a null mutation (notabilis) in tomato. We have used LeZEP1 and LeNCED1 as probes to study gene expression in leaves and roots of whole plants given drought treatments, during light/dark cycles, and during dehydration of detached leaves. During drought stress, NCED mRNA increased in both leaves and roots, whereas ZEP mRNA increased in roots but not leaves. When detached leaves were dehydrated, NCED mRNA responded rapidly to small reductions in water content. Using a detached leaf system with ABA-deficient mutants and ABA feeding, we investigated the possibility that NCED mRNA is regulated by the end product of the pathway, ABA, but found no evidence that this is the case. We also describe strong diurnal expression patterns for both ZEP and NCED, with the two genes displaying distinctly different patterns. ZEP mRNA oscillated with a phase very similar to light-harvesting complex II (LHCII) mRNA, and oscillations continued in a 48 h dark period. NCED mRNA oscillated with a different phase and remained low during a 48 h dark period. Implications for regulation of water stress-induced ABA biosynthesis are discussed. << Less

  Plant Mol Biol 42:833-845(2000) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Occurrence of the lutein-epoxide cycle in mistletoes of the Loranthaceae and Viscaceae.

  Matsubara S., Morosinotto T., Bassi R., Christian A.L., Fischer-Schliebs E., Luttge U., Orthen B., Franco A.C., Scarano F.R., Forster B., Pogson B.J., Osmond C.B.

  The lutein-epoxide cycle (Lx cycle) is an auxiliary xanthophyll cycle known to operate only in some higher-plant species. It occurs in parallel with the common violaxanthin cycle (V cycle) and involves the same epoxidation and de-epoxidation reactions as in the V cycle. In this study, the occurren ... >> More

  The lutein-epoxide cycle (Lx cycle) is an auxiliary xanthophyll cycle known to operate only in some higher-plant species. It occurs in parallel with the common violaxanthin cycle (V cycle) and involves the same epoxidation and de-epoxidation reactions as in the V cycle. In this study, the occurrence of the Lx cycle was investigated in the two major families of mistletoe, the Loranthaceae and the Viscaceae. In an attempt to find the limiting factor(s) for the occurrence of the Lx cycle, pigment profiles of mistletoes with and without the Lx cycle were compared. The availability of lutein as a substrate for the zeaxanthin epoxidase appeared not to be critical. This was supported by the absence of the Lx cycle in the transgenic Arabidopsis plant lutOE, in which synthesis of lutein was increased at the expense of V by overexpression of epsilon-cyclase, a key enzyme for lutein synthesis. Furthermore, analysis of pigment distribution within the mistletoe thylakoids excluded the possibility of different localizations for the Lx- and V-cycle pigments. From these findings, together with previous reports on the substrate specificity of the two enzymes in the V cycle, we propose that mutation to zeaxanthin epoxidase could have resulted in altered regulation and/or substrate specificity of the enzyme that gave rise to the parallel operation of two xanthophyll cycles in some plants. The distribution pattern of Lx in the mistletoe phylogeny inferred from 18S rRNA gene sequences also suggested that the occurrence of the Lx cycle is determined genetically. Possible molecular evolutionary processes that may have led to the operation of the Lx cycle in some mistletoes are discussed. << Less

  Planta 217:868-879(2003) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• FAD is a further essential cofactor of the NAD(P)H and O2-dependent zeaxanthin-epoxidase.

  Buech K., Stransky H., Hager A.

  In chloroplasts of plants the xanthophyll cycle is suggested to function as a protection mechanism against photodamage. Two enzymes catalyze this cycle. One of them, violaxanthin de-epoxidase, transforms violaxanthin (Vio) to zeaxanthin (Zea) via antheraxanthin (Anth) and is bound to the lumenal s ... >> More

  In chloroplasts of plants the xanthophyll cycle is suggested to function as a protection mechanism against photodamage. Two enzymes catalyze this cycle. One of them, violaxanthin de-epoxidase, transforms violaxanthin (Vio) to zeaxanthin (Zea) via antheraxanthin (Anth) and is bound to the lumenal surface of the thylakoid vesicles, when being in its active state. The other enzyme, Zea-epoxidase, is responsible for the backward reaction (Zea-->Anth-->Vio) and is active at the stromal side of the thylakoid. For the epoxidation of Zea this enzyme requires NAD(P)H and O2 as cosubstrates. Using isolated thylakoid membranes we found that FAD enhances the epoxidase activity (decrease of apparent Km for NAD(P)H and two-fold increase of Vmax). The flavin functions as a third cofactor which is partially lost during the isolation procedure of thylakoids. Other flavins, such as FMN or riboflavin are without effect. The involvement of FAD in the enzymatic reaction is also demonstrated by the inhibitory action of diphenyleneiodoniumchloride (DPI) (IC50 = 2.3 microM), a compound that blocks the reoxidation of reduced flavins within enzymes. The Zea-epoxidase is a multi-component enzyme system which can be classified as FAD-containing, NAD(P)H- and O2-dependent monooxygenase that is able to epoxidize 3-hydroxy beta-ionone rings of xanthophylls in the 5,6 position. << Less

  FEBS Lett. 376:45-48(1995) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.