Xanthophylls activated zeaxanthin

It is a carotenoid alcohol, and the pigment of yellow corn. However, it possesses no vitamin A activity. Zeaxanthin is widespread in nature and occurs together with xanthophyll. (Also see XANTHOPHYLL.)... 

Farber A, Young AJ, Ruban AV, Horton P and Jahns P (1997) Dynamics of xanthophyll-cycle activity in different antenna subcomplexes in the photosynthetic membranes of higher plants. The relationship between zeaxanthin conversion and nonphotochemical fluorescence quenching. Plant Physiol 115 1609-1618... 

Central to elucidating the mechanism of qE is to understand the role of the xanthophyll cycle. Eirst it is necessary to obtain information on where within the LHCII system the active xanthophyll carotenoids are bound. Information on the structural features of violaxanthin and zeaxanthin that determine their binding to LHCII is needed, just as such information is vital to understanding other allosteric effectors in... 

Fig I. Schematic of the trans-thylakoid organization of the violaxanthin cycle. De-epoxidation (VDE) and epoxidation (ZE) activities are depicted as taking place on free pigments in the lipid phase. The pigments of the xanthophyll cycle (V, A, and Z) are shown as exchanging between the lipid phase and LHCII, under light or temperature stress. It is speculated that carrier proteins may facilitate this exchange. Zeaxanthin in conjunction with the transthylakoid ApH leads to NPQ in LHCII. The role of membrane- localized protons in NPQ is controversial. 

Gruszecki WI (1990b) Violaxanthin and zeaxanthin aggregation in the lipid-water system. Stud Biophys 139 95-101 Gruszecki WI (1991) Structural characterisation ofthe aggregated forms of violaxanthin. J Biol Physics 18 99-109 Gruszecki WI (1995) Different aspects ofprotective activity of the xanthophyll cycle under stress conditions. Acta Physiol Plant 17 145-152... 

Zeaxanthin (3/f3 R)-P,p-carotene-33 -diol 33 -dihydroxy-P-carotene, a xanthophyll. At, 568.85, m.p. 206 °C (d.), isomeric with lutein one of the commonest plant pigments (yellow-orange), especially plentiful in maize and fruits of the sea buckthorn also found in algae and bacteria. It occurs free and esteri-fied as the dipalmitate, and shows no vitamin A activity. The 5,6-monoepoxide of Z., antheroxanthin, is also a common plant pigment. 

Carotenoids, structurally similar to vitamin A, are a group of more than 600 natural compounds. However, only about 50 have provitamin A activity (Olson, 1989 Palace et al, 1999). More than 60 different carotenoids have been identified in vegetable products consumed by humans (Khachik et al., 1992 Bauemfeind, 1972), and approximately 20 are present in quantifiable amounts in human semm and tissues. Hydrocarbon carotenoids (a-carotene, 3-carotene and lycopene), monohydroxy xanthophylls (e.g. P-cryptoxanthin), and dihydroxy xanthophylls (e.g. lutein and zeaxanthin) are among the main carotenoids present in human plasma and tissues (Krinsky et al, 1990). They have received considerable attention because of their various functions in human health. Most nutrition research studies have focused on the six carotenoids found in the highest concentrations in blood P-carotene, lycopene, a-carotene, lutein, zeaxanthin and P-cryptoxanthin (Basu et al., 2001). 

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