Hydroxylation carotene

Different monooxygenase enzymes hydroxylate the 3 position of the P- and s-rings of a-carotene. Hydroxylation of one ring of P-carotene produces P-cryp-toxanthin and hydroxylation of both P-rings produces zeaxanthin. Hydroxlyation... 

Fiore, A. et al.. Elucidation of the b-carotene hydroxylation pathway in Arabidopsis thahana, FEBS Lett. 580, 4718, 2006. 

Fiore A, Dall Osto L, Cazzaniga S, Diretto G, Giuliano G, Bassi R. A quadruple mutant of Arabidopsis reveals a P-carotene hydroxylation activity for LUT1/CYP97C1 and a regulatory role of xanthophylls on determination of the PSl/PSll ratio. BMC Plant Biol. 2012 Apr 18 12 50. 

The oxidation of carotenes results in the formation of a diverse array of xanthophylls (Fig. 13.7). Zeaxanthin is synthesised from P-carotene by the hydroxylation of C-3 and C-3 of the P-rings via the mono-hydroxylated intermediate P-cryptoxanthin, a process requiring molecular oxygen in a mixed-function oxidase reaction. The gene encoding P-carotene hydroxylase (crtZ) has been cloned from a number of non-photosynthetic prokaryotes (reviewed by Armstrong, 1994) and from Arabidopsis (Sun et al, 1996). Zeaxanthin is converted to violaxanthin by zeaxanthin epoxidase which epoxidises both P-rings of zeaxanthin at the 5,6 positions (Fig. 13.7). The... 

Replacement of the hydrogen at the 3 or 3 position of the carotene ring with a hydroxyl is the next step in both branches of the pathway. Hydroxylation of the rings of the carotenes leads to biosynthesis of the xanthophylls, including the well-known lutein and zeaxanthin food pigments. Lutein is formed by hydroxylation of a-carotene zeaxanthin is formed by hydroxylation of P-carotene. 

Hydroxyl groups — Since conjugated hydroxyl groups do not have any influence on the chromophore of the molecule, they do not have any effect on the UV-Vis spectrum. Therefore, p-carotene, p-cryptoxanthin, and zeaxanthin all... 

Note Rp-values (p-carotene = 100) are used for systems 1 to 3 and Rp values for system 4. Solvent compositions by volume, p.e. = petroleum ether (40 to 60°C) DB indicates number of in chain conjugated double bonds FG indicates functional groups E = epoxy, H = hydroxyl, K = ketone. 

Carotenoids are a group of more than 750 naturally occurring molecules (Britton et al. 2004) of which about 50 occur in the normal human food chain. Of these, only 24 have, so far, been detected in human plasma and tissues (Khachik et al. 1995), with only six molecules being abundant in normal human plasma (for chemical formulas see Figure 13.1). Carotenoids are subdivided into two main classes the carotenes, cyclized (e.g., P-carotene) or uncyclized (e.g., lycopene) hydrocarbons, and the xanthophylls, which have hydroxyl groups (e.g., lutein and zeaxanthin), keto-groups (e.g., canthaxanthin), or both (e.g., astaxanthin) as functional groups. 

Carotenoids are hydrophobic molecules and thus are located in lipophilic sites of cells, such as bilayer membranes. Their hydrophobic character is decreased with an increased number of polar substitutents (mainly hydroxyl groups free or esterified with glycosides), thus affecting the positioning of the carotenoid molecule in biological membranes. For example, the dihydroxycarotenoids such as LUT and zeaxanthin (ZEA) may orient themselves perpendicular to the membrane surface as molecular rivet in order to expose their hydroxyl groups to a more polar environment. In contrast, the carotenes such as (3-C and LYC could position themselves parallel to the membrane surface to remain in a more lipophilic environment in the inner core of the bilayer membranes (Parker, 1989 Britton, 1995). Thus, carotenoid molecules can have substantial effects on the thickness, strength, and fluidity of membranes and thus affect many of their functions. 

TV Relatively large amounts of fi.fi-carotene and hydroxyl derivatives... 

Rodriguez DB, Tanaka Y, Katayama T, Simpson KL, Lee T-C and Chichester CO. 1976. Hydroxylation of 3-carotene on micro-cel C. J Agric Food Chem 24 819-822. 

Lutein has a stucture similar to beta-carotene with a hydroxyl group on the ionone ring at each end of the molecule. It is somewhat less sensitive to oxidation and heat degradation than beta-carotene. It contributes a yellow color. 

Takaichi, S., K. Shimada, and J.-I. Ishidsu. 1990. Carotenoids from the aerobic photosynthetic bacterium Erytkrobacter longus P-carotene and its hydroxyl derivatives. Archives of Microbiology 153 118-122. 

Reversed-phase liquid chromatography shape-recognition processes are distinctly limited to describe the enhanced separation of geometric isomers or structurally related compounds that result primarily from the differences between molecular shapes rather than from additional interactions within the stationary-phase and/or silica support. For example, residual silanol activity of the base silica on nonend-capped polymeric Cis phases was found to enhance the separation of the polar carotenoids lutein and zeaxanthin [29]. In contrast, the separations of both the nonpolar carotenoid probes (a- and P-carotene and lycopene) and the SRM 869 column test mixture on endcapped and nonendcapped polymeric Cig phases exhibited no appreciable difference in retention. The nonpolar probes are subject to shape-selective interactions with the alkyl component of the stationary-phase (irrespective of endcapping), whereas the polar carotenoids containing hydroxyl moieties are subject to an additional level of retentive interactions via H-bonding with the surface silanols. Therefore, a direct comparison between the retention behavior of nonpolar and polar carotenoid solutes of similar shape and size that vary by the addition of polar substituents (e.g., dl-trans P-carotene vs. dll-trans P-cryptoxanthin) may not always be appropriate in the context of shape selectivity. 

Carotenes can be hydroxylated and otherwise modified in a number of ways.110/128-131 The structure of zeaxanthin, one of the resulting xanthophylls, is indicated in Fig. 22-5. Some other xanthophylls are shown in Eq. 22-10. Lutein resembles zeaxanthin, but the ring at one end of the chain has been isomerized by a shift in double bond position to the accompanying structure. The photosynthetic bacterium Rho-dospirillum rubrum has its own special carotenoid spirilloxanthin, which has the accompanying structure at both ends of the chain. 

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