Pathway carotenal

ERNST s and sandmann g (1988) Poly-c carotene pathway in the Scenedesmus mutant C-6D , Arch Microbiol, 150, 590-94. 

Ernst, S. and Sandmann, G., Poly-cis carotene pathway in Scenedesmus mutant C-6D, Arch. Microbiol. 150, 590, 1988. 

Spirilloxanthin pathway (normal spirilloxanthin, unusual spirilloxanthin, spheroidene, and carotenal pathways). 

The Chromatiaceae have either the spirilloxanthin pathway (normal spirilloxanthin, unusual spirilloxanthin and carotenal pathways) or okenone of the okenone pathway except for one species, Tea. halophila, which has both pathways (Tables 1 and4). Even in the same genus, some species have the spirilloxanthin pathway and others have the okenone pathway. Therefore, the carotenogenesis pathways are not well related to the bacteria s classification in the Chromatiaceae. 

The Chloroflexaceae only have the y- and jS-carotene pathway (Tables 1 and 7). In Chloroflexus, most of carotenes and BChl c are located in the chlorosomes, which are very similar to those of the Chlorobiaceae, while the carotenoid glucoside esters, which are also found, are mainly located in the membranes and the envelope of chlorosomes (Tsuji et al., 1995). Except for Chloroflexus, analysis of carotenoids in this group needs a lot more work. 

Vitamins are classified by their solubiUty characteristics iato fat-soluble and water-soluble groups. The fat-soluble vitamins A, E, and K result from the isoprenoid biosynthetic pathway. Vitamin A is derived by enzymic cleavage of the symmetrical C q beta-carotene, also known as pro-vitamin A. Vitamins E and K result from condensations of phytyldiphosphate (C2q) with aromatic components derived from shikimic acid. Vitamin D results from photochemical ring opening of 7-dehydrocholesterol, itself derived from squalene (C q). 

BARTLEY G E, SCOLNIK p A and BEYER p (1999) Two Arabidopsis thaliana carotene desaturases, ph)4oene desaturase and zeta-carotene desaturase, expressed in EicAencA/a coli, catalyze a poly-cis pathway to yield pro-lycopene , Eur JBiochem, 259, 396-403. 

MORSTADT L, GRABER P, DE PASCALIS L, KLEINIG H, SPETH V and BEYER P (2002) Chemiosmotic ATP synthesis in photo synthetically inactive chromoplasts from Narcissus pseudonarcissus L. linked to a redox pathway potentially also involved in carotene desaturation , Planta, 215, 132-40. 

RONEN G, CARMEL-GOREN L, ZAMIR D and HIRSCHBERG J (2000) An alternative pathway to 13-carotene formation in plant chromoplast discovered by map-based cloning of beta and old-gold color mutations in tomato , Proc Natl Acad Sci, 97, 11102-7. 

YE X, AL-BABILI s, KLOTZ A, ZHANG J, LUCCA p, BEYER p and POTRYKUS I (2000) Engineering provitamin A ( 3-carotene) biosynthesis pathway into (carotenoid-free) rice endosperm . Science, 287, 303-5. 

FIGURE 3.2.2 Metabolic pathways of carotenoids such as p-carotene. CM = chylomicrons. VLDL = very low-density lipoproteins. LDL = low-density lipoproteins. HDL = high-density lipoproteins. BCO = p-carotene 15,15 -oxygenase. BCO2 = p-carotene 9, 10 -oxygenase. LPL = lipoprotein lipase. RBP = retinol binding protein. SR-BI = scavenger receptor class B, type I. 

Carotene cleavage enzymes — Two pathways have been described for P-carotene conversion to vitamin A (central and eccentric cleavage pathways) and reviewed recently. The major pathway is the central cleavage catalyzed by a cytosolic enzyme, p-carotene 15,15-oxygenase (BCO EC 1.13.1.21 or EC 1.14.99.36), which cleaves p-carotene at its central double bond (15,15 ) to form retinal. Two enzymatic mechanisms have been proposed (1) a dioxygenase reaction (EC 1.13.11.21) that requires O2 and yields a dioxetane as an intermediate and (2) a monooxygenase reaction (EC 1.14.99.36) that requires two oxygen atoms from two different sources (O2 and H2O) and yields an epoxide as an intermediate. ... 

The second pathway is the eccentric cleavage that occurs at double bonds other than the central 15,15 -double bond of the P-carotene molecule to produce different products called P-apocarotenals with various chain lengths. Because only trace amounts of apocarotenals were detected in vivo from tissues of animals fed P-carotene and these compounds can be formed non-enzymatically from P-carotene auto-oxidation, the existence of this pathway was controversial until recently. The identification of P-carotene 9, 10 -oxygenase (BC02), which acts specifically at the 9, 10 double bond of P-carotene to produce P-apo-lO -carotenal and P-ionone, provided clear evidence of the eccentric cleavage pathway in vivo. Lycopene was also reported as a substrate for BC02 activity. 

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. 

In a very recent study in potatoes, inhibition of LCYE accumulation was accomplished by an antisense LcyE driven by the patatin promoter and allowed rechanneling of lycopene toward the P-carotene branch of the pathway to produce up to 14-fold increased levels of P-carotene as well as up to 2.5-fold increased total carotenoids. RNAi and TILLING for manipulation of carotenogenesis have yet to be reported, but these new techniques for suppression of function and generation and selection of allelic diversity are likely to impact future research and production of varieties with enhanced pigment accumulation. 

Hausmann, A. and Sandmann, G., A single five-step desaturase is involved in the carotenoid biosynthesis pathway to beta-carotene and torulene in Neurospora crassa, Eungal Genet. Biol. 30, 147, 2000. 

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

Ye, X. et al.. Engineering the provitamin A (beta-carotene) biosynthetic pathway into (carotenoid-free) rice endosperm. Science 287, 303, 2000. 

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