Xanthophylls identifying

Monarch epidermis. Peaks seen at 8.7, 10, and 82min are 3-hydroxy-10 -apo-P-carotenal, lutein, zeaxanthin, and P-carotene, respectively. The peak seen eluting at 22 min is the internal standard, monopropyl lutein ether, (b) The chromatogram obtained from an extract of the leaves of the milkweed plant. Peaks eluting prior to lutein are xanthophylls and epoxy xanthophylls, identified components include lutein, zeaxanthin, P-carotene, and its crT-isomer, eluting at 10, 11, 41, 77, and 79min, respectively. 

Like all the photosynthetic organisms of the brown lineage, Chrysophyceae contain chlorophyll a and perhaps chlorophylls c, but this situation does not seem to have been definitively established (Morris, 1968 Meeks, 1974). P-Carotene is always present, and the majority of xanthophylls are fiicoxanthin, diatoxanthin, and diadinoxanthin (Liaaen-Jensen, 1978 Withers et al, 1981). Some minor xanthophylls identified in several species have been gathered together in Appendix lO.A. 

Stndies of the antoxidation of carotenoids in liposomal suspensions have also been performed since liposomes can mimic the environment of carotenoids in vivo. Kim et al. stndied the antoxidation of lycopene," P-carotene," and phytofluene" " in liposomal snspensions and identified oxidative cleavage compounds. Stabilities to oxidation at room temperature of various carotenoids incorporated in pig liver microsomes have also been studied." The model took into account membrane dynamics. After 3 hr of reactions, P-carotene and lycopene had completely degraded, whereas xanthophylls tested were shown to be more stable. 

Identifying electronic and vibrational properties of xanthophylls should provide not only structural information. Gaining information about excited state energy levels would help to design and interpret kinetic experiments, which probe molecular interactions and the energetic relationship between the xanthophylls and chlorophylls. 

The chemical composition of the macular yellow pigment was originally characterized by Wald as being a leaf xanthophyll carotenoid (Wald 1945). It took another 40 years until the molecules lutein and zeaxanthin were identified as its main constituents by Bone et al. (1985), and in 1993 the same authors reported that macular zeaxanthin is itself comprised of two stereoisomers, (3/f,37f)-/eaxan(hin and (3/f,3. S )-/eaxan(hin (Bone et al. 1993), this compound will be called (meso)-zeaxanthin throughout this article. These three molecules are often collectively called the macular xanthophylls (for their chemical formulas see Figure 13.2). 

Apart from lutein and zeaxanthin, a number of other xanthophylls are present in the retina at low concentrations, including 3 -cpi-lutein, lactucaxanthin, 3 -dehydrolutein, and (3,(3-carotene-3,3 -dione (Khachik et al. 1997a, Bernstein et al. 2001). Interestingly, (3-carotene, the provitamin A precursor of the chromophore of the visual pigments, has only been identified in traces in the retina, if at all. 

However, the metabolic pathways of lutein and zeaxanthin are only beginning to be discovered. Several derivatives of dietary xanthophylls have been identified in the retina, such as 3 -epilutein, meso-zeaxanthin, 3 -oxolutein, and 3-methoxyzeaxanthin, and it has been suggested that they may be formed as a result of nonenzymatic oxidative modifications (Bernstein et al., 2001,2002b Bhosale et al., 2007b Khachik et al., 1997). The macula lutea contains predominantly meso-zeaxanthin (Figure 15.1), which is believed to originate from either oxidative modification or double bond isomerization of dietary lutein (Khachik et al., 1997, 2002). 

It is of interest that carotenoid pigments (xanthophylls), sterols (spinasterol and chondrillasterol) and a triterpene alcohol have been identified in cucurbit seed oil (31, 3 , 37L However, cucurbit oils such as that from Buffalo gourcT are amenable to refining, bleaching and deodorizing (38). 

ICGA is most valuable for evaluation of choroidal neovascularization. Fluorescein angiography of early choroidal fluorescence is potentially inhibited by media opacities, fundus pigmentation, xanthophyll, RPE, hemorrhage, or serous exudate in the retina. Rapid leakage from the fenestrated choroidal capillaries is sometimes not easily appreciated with fluorescein angiography in attempting to identify subretinal CNVMs. 

Immediately cork the tube filled with nitrogen and then add a drop or two of dichloromethane to dissolve the pigments for TLC analysis. Carry out the analysis without delay by spotting the mixture on a TLC plate about 1 cm from the bottom and 8 mm from the edge. Make one spot concentrated by repeatedly touching the plate, but ensure that the spot is as small as possible—less than 1.0 mm in diameter. The other spot can be of lower concentration. Develop the plate with 70 30 hexane acetone. With other plates try cyclohexane and toluene as eluents and also hexane/ethanol mixtures of various compositions. The container in which the chromatography is carried out should be lined with filter paper that is wet with the solvent so the atmosphere in the container will be saturated with solvent vapor. On completion of elution, mark the solvent front with a pencil and outline the colored spots. Examine the plate under the uv light. Are any new spots seen Report colors and i /values for all of your spots, and identify each as lycopene, carotene, chlorophyll, or xanthophyll. 

Triterpenoid Carotenoids. Two novel triterpenoid xanthophylls from Streptococcus faecium have been identified " as 4,4 -diapo-7, 8 -dihydro-i/, / -caroten-4-al (16) and 4,4 -diapo-i/, A-caroten-4-al (17). Two other C30 carotenoids, jS-citraurinene 8 -apo-/S-caroten-3-ol (18)] and /8-citrauroP [8 -apo-/3-carotene-3,8 -diol (19)], both isolated from citrus fruits, are likely to be derived from C40 carotenoids. Spectroscopic data were presented for both compounds. 

Niyogi KK, Bjorkman O and Grossman AR. (1997). Chlamydomonas xanthophyll cycle mutants identified by video imaging of chlorophyll fluorescence quenching. Plant Cell 9,1369-1380. 

The term carotenoids designates a group of structurally related colorants that are mainly found in plants. At present, more than 600 carotenoids have been identified. Their basic structure is a symmetrical tetraterpene skeleton, formed by head-to-tail condensation of two 20-carbon units. (Formula 9.1). Based on their composition, carotenoids are subdivided into two groups carotenes, which contain only carbon and hydrogen atoms, e.g., a-, P-, and y-carotenes and lycopene (Formulae 9.2-9.4) and xanthophylls — oxocarotenoids — which contain at least one oxygen function, such as hydroxy, keto, or epoxy groups (Formulae 9.5-9.9). 

Prior to 1995, only one locus affecting Xanthophyll biosynthesis in photosynthetic tissues of Arabidopsis had been identified, the ABA i locus, the mutation of which disrupts zeaxanthin deepoxidase, one of two xanthophyll cycle enzymes (Koomneef et al, 1982 Rock and Zeevaart, 1991 Rock et al., 1992). As a step toward advancing understanding of xanthophyll biosynthesis, incorporation, and function in plants, the author s laboratory has screened for and identified mutations defining two additional loci required for xanthophyll biosynthesis in Arabidopsis, LUTl and LUT2 LUT= LUTein deficient). Mutations at either locus result in defects in the synthesis of lutein, the most predominant xanthophyll in plants. Singly and in combination with the aba mutation, these lut mutations have allowed the genetic construction of five distinct mutant lines which differ dramatically in their carotenoid composition relative to wild-type Arabidopsis. In the remainder of this chapter I will first briefly discuss the aba mutation followed by a... 

An atomic resolution model of the plant lightharvesting complex LHC-II has been published (Kiihlbrandt, 1994 Ktihlbrandt et al., 1994 Hunter et al., 1994b). Two xanthophyll molecules are located at the eenter of the complex and were identified as lutein based on the fact that this pigment is the most abundant. They apparently have a structural role in addition to their triplet quenching ability (Plumley and Schmidt, 1987 Paulsen et al., 1990 Heinze et al., 1997). The main xanthophylls are lutein, neoxanthin, and violaxanthin (Siefermann-Harms, 1985, 1990a). Time-resolved optical spectroscopy showed that at least two spectroscopically distinct xanthophylls participate in triplet quenching, apparently lutein and violaxanthin (Peterman et al., 1995, 1997). 

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