This Article Full Text Full Text (PDF) All Versions of this Article: 138/1/421    most recent pp.104.057992v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Web of Science (15) Citing Articles via Google Scholar Google Scholar Articles by Gandía-Herrero, F. Articles by García-Carmona, F. Search for Related Content PubMed PubMed Citation Articles by Gandía-Herrero, F. Articles by García-Carmona, F. Agricola Articles by Gandía-Herrero, F. Articles by García-Carmona, F.

BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Betaxanthins as Substrates for Tyrosinase. An Approach to the Role of Tyrosinase in the Biosynthetic Pathway of Betalains¹

Departamento de Bioquímica y Biología Molecular A, Unidad Docente de Biología, Facultad de Veterinaria, Universidad de Murcia, E–30100 Espinardo, Murcia, Spain

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 + H]⁺) 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 = 84.3 µM). 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.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.057992.

^* Corresponding author; e-mail pepa{at}um.es; fax 34–968–364147.

Received December 10, 2004; returned for revision February 1, 2005; accepted February 3, 2005.

This article has been cited by other articles:

				M. A. Escobar, A. Shilling, P. Higgins, S. L. Uratsu, and A. M. Dandekar Characterization of Polyphenol Oxidase from Walnut J. Amer. Soc. Hort. Sci., November 1, 2008; 133(6): 852 - 858. [Abstract] [Full Text] [PDF]