Umwandlung eines Betacyans in ein Betaxanthin Synthese von Indicaxanthin aus Betanin

2010

Planta

172

177

Betalains are water-soluble pigments with high antiradical capacity which bestow bright colors on flowers and fruits of most plants of the order Caryophyllales. They are classified as betacyanins, exhibiting a violet coloration, and betaxanthins, which exhibit yellow coloration. Traditionally, betalains have been defined as condensation products of betalamic acid with different amines and amino acids, but the implication of the pigment structure for their properties has not been investigated. This paper explores different structural features of the betalains, revealing the clues for the switch from yellow to violet color, and the loss of fluorescence. A relevant series of 15 betalain-related compounds (both natural and novel semisynthetic ones) is obtained and characterized by chromatography, UV-vis spectrophotometry, fluorescence, and electrospray ionization mass spectroscopy. Antiradical properties of individual pure compounds in a broad pH range are studied under the ABTS(*+) radical assay. Relevance of specific bonds is studied, and differences between betaxanthins and betacyanins are used to explore in depth the structure-antiradical activity relationships in betalains.

Section: Extraction and Semi-synthesis Of Betalainsmentioning

confidence: 99%

Structural implications on color, fluorescence, and antiradical activity in betalains

2010

Planta

172

177

“…Synthetic betaxanthins were obtained as immonium condensation products of betalamic acid with (S)-forms of the amino acids DOPA and Tyr, as described by Wyler et al (1965), with some modifications. Briefly, aliquots of a 0.15 mM betanin:isobetanin mixture (95:5) purified from red beet extracts were used as a source of betalamic acid.…”

Section: Betaxanthin (Dopaxanthin and Tyr-betaxanthin) Semisynthesismentioning

confidence: 99%

Betaxanthins as Substrates for Tyrosinase. An Approach to the Role of Tyrosinase in the Biosynthetic Pathway of Betalains

2005

Plant Physiology

Tyrosinase or polyphenol oxidase (EC 1.14.18.1) is the key enzyme in melanin biosynthesis and in the enzymatic browning of fruits and vegetables. The role of tyrosinase in the secondary metabolism of plants still remains unclear, but its implication in betalain biosynthesis has been proposed. Betalains are an important class of water-soluble pigments, characteristic of plants belonging to the order Caryophyllales. In this article, the betaxanthins, tyrosine-betaxanthin (portulacaxanthin II) and dopaxanthin, are reported to be physiological substrates for tyrosinase. The direct activity of tyrosinase on selected betaxanthins is characterized in depth, and conversion of tyrosine-betaxanthin to dopaxanthin and its further oxidation to a series of compounds are described. Identity of the reaction products was studied by high-performance liquid chromatography and electrospray ionization-mass spectrometry. Masses determined for the reaction products were the same in all cases, 389 m/z ([M 1 H] 1 ) and equal to that determined for betanidin. Data indicate that dopaxanthin-quinone is obtained and evolves to more stable species by intramolecular cyclization. Kinetic parameters for tyrosinase acting on dopaxanthin were evaluated, showing a high affinity for this substrate (K m 5 84.3 mM). The biosynthetic scheme of betalains is reviewed and a branch is proposed based on the description of physiological substrates for tyrosinase. Lampranthus productus, Glottiphylum oligocarpum, and Glottiphylum pigmaeum are described as sources of stereopure (2S/S)-dopaxanthin.Tyrosinase or polyphenol oxidase (monophenol, o-diphenol:oxygen oxidoreductase; EC 1.14.18.1) is a copper enzyme that catalyzes two different reactions using molecular oxygen: the hydroxylation of monophenols to o-diphenols (monophenolase activity) and the oxidation of the o-diphenols to o-quinones (diphenolase activity; Sánchez-Ferrer et al., 1995). This enzyme is widely distributed in plants, microorganisms, and animals where tyrosinase is responsible for melanization.A wide variety of plant tyrosinase behaviors has been described and reviewed (Mayer and Harel, 1991;van Gelder et al., 1997). A molecular oxygenscavenging function in the chloroplast (Vaughn et al., 1988) and a role in plant defense (Constabel et al., 1995) have been suggested. Its implication in the secondary metabolism of betalains has been proposed (Steiner et al., 1999), but the physiological function of tyrosinase in higher plants is yet to be fully determined.Betalains are water-soluble nitrogen-containing pigments that are present in plants belonging to the order Caryophyllales (Strack et al., 2003) and in the fungal genera Amanita (Musso, 1979) and Hygrocybe (von Ardenne et al., 1974). All betalain pigments contain betalamic acid as the chromophore. Depending upon the nature of the betalamic acid addition residue, the betalains can be classified as either betacyanins or betaxanthins. Betacyanins contain a cyclo-3,4-dihydroxyphenylalanine (cyclo-DOPA; usually glycosylated) residue and exhibit ...

“…These pigments were synthesized by a Schiff condensation reaction between the aldehyde group of betalamic acid and the amine group of the corresponding amines (Wyler et al 1965;Trezzini and Zry¨d 1991;Schliemann et al 1999;Stintzing et al 2002). Semi-syntheses were started from aliquots of purified betanin, extracted from red beet extracts.…”

Section: Chemical Synthesis and Purification Of Betaxanthins Derived mentioning

confidence: 99%

“…Tyramine-betaxanthin and dopamine-betaxanthin semi-synthesis Synthetic betaxanthins were obtained as immonium condensation products of betalamic acid with the amines tyramine and dopamine, as described by Wyler et al (1965), with some modifications. Briefly, betanin was used as a source of betalamic acid.…”

Section: Chemicalsmentioning

confidence: 99%

Characterization of the monophenolase activity of tyrosinase on betaxanthins: the tyramine-betaxanthin/dopamine-betaxanthin pair

2005

Planta

Tyrosinase or polyphenol oxidase (EC 1.14.18.1) is the key enzyme responsible for melanin biosynthesis and for the enzymatic browning of fruits and vegetables. Although the function of tyrosinase in the secondary metabolism of plants remains unclear, it has been proposed that the enzyme plays a role in the betalain biosynthetic pathway. Betalains are an important class of water-soluble pigments, characteristic of plants belonging to the order Caryophyllales. In the present work, the betaxanthins tyramine-betaxanthin (miraxanthin III) and dopamine-betaxanthin (miraxanthin V) are reported as new natural substrates for tyrosinase. The result of the diphenolase activity of the enzyme on dopamine-betaxanthin was a series of products identified by HPLC and ESI-MS as quinone-derivatives. Data indicate that dopamine-betaxanthin-quinone is obtained and evolves to more stable species by intramolecular cyclization. The kinetic parameters evaluated for the diphenolase activity were V(m) = 74.4 microM min(-1), K(m) = 94.7 microM. Monophenolase activity on tyramine-betaxanthin yielded the same compounds in the absence of a reducing agent, but when ascorbic acid was present enzymatic conversion to dopamine-betaxanthin could be found. For the first time, kinetic characterization of the monophenolase activity of tyrosinase on betaxanthins is provided (V(m) = 10.4 microM min(-1) and K(m) = 126.9 microM) and a lag period is described and analyzed according to the mechanism of action of the enzyme. The high affinity shown by tyrosinase for these substrates may be indicative of a previously unconsidered physiological role in betalain metabolism. A possible mechanism for the formation of 2-descarboxy-betacyanins from tyramine-betaxanthin by tyrosinase is also discussed.