This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: crocin biosynthesis
|Superclasses:||Biosynthesis → Secondary Metabolites Biosynthesis → Terpenoids Biosynthesis → Tetraterpenoids Biosynthesis → Apocarotenoids Biosynthesis|
Saffron is characterized by its color, bitter taste and fragrance. All three attributes of this extremely expensive spice are due in large part to products of the degradation of the carotenoid zeaxanthin. The color is mainly due to a number of carotenoid glycosides derived from crocetin (this pathway). In contrast, picrocrocin is largely responsible for the bitter taste of this spice, whereas safranal is at the main constituent of its aroma (see crocetin biosynthesis). Crocetin is an insoluble aglycone compound, which, through sequential glucosylation, is converted to the soluble crocin. It is this carotenoid dye that gives food a rich golden-yellow hue. Crocetin can be converted by saffron cell suspension cultures into several glycosyl esters, which, in addition to those shown on the pathway diagram, include esters of the rare trisaccharide neapolitanose (O-β-D-glucopyranosyl-(1->2)-O-[β-D-glucopyranosyl-(1->6)]-β-D-glucose) in the compounds crocetin dineapolitanose ester, crocetin neapolitanose gentiobiosyl ester and crocetin neapolitanose glucosyl ester [Cote00a]. Finally, although this pathway only present the most common all-trans compounds, cis isomers have also been identified [Carmona06, Cote00a]. In vivo, crocin is the most abundant pigment found in the stigma of saffron and the fruit of Gardenia jasmonoides [Carmona06, Pfister96].
Enzymes of the pathway:
Several enzymes have been identified that catalyze the glucosylation of crocetin. The only one, however, that has been cloned is the Crocus sativus crocetin glucosyltransferase [Moraga04]. This enzyme was shown to catalyze the glucosylation of crocetin. Although the exact nature of the products formed by this enzyme remain to be unequivocally confirmed, the enzyme was shown to catalyze specifically the glucosylation of crocetin, β-D-glucosyl crocetin and β-D-gentiobiosyl crocetin [Moraga04]. It is currently believed that more than one glucosyltransferase catalyze the glucosylation of crocetin [Cote00].
Two UDP-glucose: crocetin glucosyltransferases identified and characterized from cell cultures of Gardenia jasminoides were able to sequentially glucosylate the aglycon crocetin and all the subsequent mono- and diglucosylated intermediates to the final product of the pathway, i.e. crocin. It was demonstrated that the crocetin glucosyltransferase UGT75L6 glucosylated the free carboxyl groups of crocetin and monoglucosylated and gentiobioside intermediates while the crocetin ester glucosyltransferase UGT94E5 catalyzed the β1 to β6 glucosylation of the intermediates generating the corresponding gentio- and digentiobosyl ester of crocetin [Nagatoshi12].
Carmona06: Carmona M, Zalacain A, Sanchez AM, Novella JL, Alonso GL (2006). "Crocetin esters, picrocrocin and its related compounds present in Crocus sativus stigmas and Gardenia jasminoides fruits. Tentative identification of seven new compounds by LC-ESI-MS." J Agric Food Chem 54(3);973-9. PMID: 16448211
Cote00a: Cote F. (2000). "Purification et caractérisation d'une UDP-glucose:crocétine 8,8'-glucosyltransférase impliquée dans la synthèse de la crocine à partir de cultures cellulaires de safran(Crocus sativus L.)." Thèse présentée à la Faculté des sciences de l'agriculture et de l'alimentation Université Laval Québec.
Moraga04: Moraga AR, Nohales PF, Perez JA, Gomez-Gomez L (2004). "Glucosylation of the saffron apocarotenoid crocetin by a glucosyltransferase isolated from Crocus sativus stigmas." Planta 219(6);955-66. PMID: 15605174
Nagatoshi12: Nagatoshi M, Terasaka K, Owaki M, Sota M, Inukai T, Nagatsu A, Mizukami H (2012). "UGT75L6 and UGT94E5 mediate sequential glucosylation of crocetin to crocin in Gardenia jasminoides." FEBS Lett 586(7);1055-61. PMID: 22569263
Pfister96: Pfister S, Meyer P, Steck A, Pfander H (1996). "Isolation and Structure Elucidation of Carotenoid-Glycosyl Esters in Gardenia Fruits (Gardenia jasminoides Ellis) and Saffron (Crocus sativus Linne)." J. Agric. Food Chem. 44(6):2612-2615.
Cote01: Cote F., Cormier F., Dufresne C., Willemot C. (2001). "A highly specific glucosyltransferase is involved in the synthesis of crocetin glucosylesters in Crocus sativus cultured cells." J. Plant Physiol. 158:553-560.
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