P cyclase

P-cyclase (CrtL-h) and P-carotene hydroxylase (b-Chy) (fhiit specific) carotene, P-cryptoxanthin and zeaxanthin 2002... 

PECKER I, GUBBAY R, CUNNINGHAM F X Jr and HIRSCHBERG Y (1996) Cloning and characterisation of the cDNA for lycopene P-cyclase from tomato reveals a decrease in its expression during tomato ripening , Plant Mol Biol, 30, 806-19. 

A series of desaturation reactions convert phytoene to i -carotene and then to lycopene, the important red pigment in tomatoes. In pepper, lycopene undergoes a cyclization reaction on both ends by lycopene P-cyclase, thus producing P-carotene (Fig. 8.2) [25]. Beta-carotene is then converted to -cryptoxanthin, zeaxanthin. 

PECKER, L, GABBAY, R., CUNNINGHAM JR., F. X., HIRSCHBERG, J., Cloning and characterization of the cDNA for lycopene p-cyclase from tomato reveals decrease in its expression during fruit ripening.. Plant Mol. Bio. 1996, 30, 807-819. 

Fig. 8.16 Pathways for the production of hydroxylated carotenoids in . coli. Isopentenyl pyrophosphate (IPP) and farnesyl diphosphate (FPP) are produced via internal methylerythritol phosphate (MEP) pathway and FPP synthase. CrtE GGPP synthase, CrtB phytoene synthase, CrtI phytoene dehydrogenase, LycB lycopene p-cyclase, LycE lycopene e-cyclase...

First, the main kiwifruit carotenoids were lutein (6) and P-carotene (2) during the kiwifruit development. Their levels of P-carotene (2) was controlled by the transcriptional activity of the lycopene P-cyclase gene. Then, the content of P-carotene (2) increased rapidly when kiwifruit was maturated and ripened (Figure 1). 

D Ambrosio G, Griorio G, Marino 1, Merendino A, Petrozza A, Salfi L, Stigliani AL, Cellini F (2004) Virtually complete conversion of lycopene into P-carotene in fruits of tomato plants transformed with the tomato lycopene P-cyclase (tlcy-b) cDNA. Plant Sci 166 207-214... 

Guo F, Zhou W, Zhang J, Xu Q, Deng X (2012) Effect of the citms lycopene P-cyclase transgene on carotenoid metabolism in transgenic tomato fruits. PLoS One 7 e32221... 

Carotenoid pathway continues with the cyclization of lycopene, involving the formation of 6C cyclic end groups. Two major enzymes participate at this point lycopene-p-cyclase (LCY-B) and lycopene-8-cyclase (LCY-E). Unusually, tomato contains two lycopene p-cyclases, LCY-B [33] as described above, and also CYC-B, a chromoplast-specific cyclase that would play a major role in carotenoid accumulation in fruits [34]. Lycopene p-cyclase forms initially y-carotene which only accumulates to traces in ripe fruits as a second p-ring is added by the same enzyme to yield p-carotene. 

Following the opposite approach, plants overexpressing lycopene p-cyclase (LCY-B) cDNA resulted in high contents of beta-carotene at the expense of lycopene, which was almost completely cyclized [94]. The plants did not show collateral effects, instead showed an increased productivity. Total carotenoid content was also increased in some progenies and beta-carotene content was twofold that of the beta mutant. 

The metabolic engineering of xanthophyll contents in tomato has also been tried. The overexpression of lycopene p-cyclase (LCY-B) and a Capsicum p-carotene hydroxylase (B-CHY) using the fruit-specific pds promoter resulted in increased... 

Two cyanobacteria also contain these enzymes (Table 106.3). Synechococcus elongatus PCC 7942 contains a functional CrtL [38]. Prochlorococcus marinus MED4 contains two lycopene cyclases, CrtL-b and CrtL-e. CrtL-b exhibits lycopene p-cyclase activity, whereas CrtL-e is a bifunctional enzyme having both lycopene s-cyclase and lycopene (3-cyclase activities [39]. The combination of these two cyclases allows the production of (3-carotene, a-carotene, and E-carotene. Both enzymes might have originated from the dupUcation of a single gene. The characteristics of this CrtL-e are somewhat different from those observed in land plants [40]. 

Ramos A, Coesel S, Marques A, Rodrigues M, Baumgartner A, Norinda J, Rauter A, Brenig B, Varela J (2008) Isolation and characterization of a stress-inducible Dunaliella salina Lcy-j3 gene encoding a functional lycopene P-cyclase. Appl Microbiol Biotechnol 79 819-828... 

Peck RF, Johnson EA, Krebs MP (2002) Identification of a lycopene P-cyclase required for bacteriorhodopsin biogenesis in the archaeon Halobacterium salinarum. J Bacteriol 184 2889-2897... 

Hemmi H, Bcejiri S, Nakayama T, Nishino T (2003) Fusion-type lycopene P-cyclase from a thermoacidophilic archaeon Sulfolobus solfataricus. Biochem Biophys Res Coiiunun 305 586-591... 

Tao L, Yao H, Kasai H, Misawa N, Oieng Q (2006) A carotenoid synthesis gene cluster from Algoriphagus sp. KK10202C with a novel fusion-type lycopene P-cyclase gene. Mol Gen Genomic 276 79-86... 

Figure 3. Carotenoid biosynthesis in plants. Enzyme abbreviation El - phytoene synthase E2 -phytoene desaturase E3 - -carotene isomerase E4 - -carotene desaturase E5 - lycopene e-cyclase E6 - lycopene p-cyclase E7 -s-carotene hydroxylase E8 - P-ring hydroxylase E9 -p-carotene hydroxylase E10 -s-ringhydroxylase Ell - p-caroteneketolase.

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