Characterization of recombinant Beta vulgaris 4,5-DOPA-extradiol-dioxygenase active in the biosynthesis of betalains.

Betalains are water-soluble pigments with high antiradical capacity which bestow bright colors to flowers, fruits and other parts of most plants of the order Caryophyllales. The formation of the structural unit of all betalains, betalamic acid from the precursor amino acid 4,5-dihydroxyphenylalanine is catalyzed by the enzyme 4,5-DOPA-extradiol-dioxygenase followed by intramolecular cyclization of the 4,5-secodopa intermediate. This paper describes the purification and the molecular and functional characterization of an active 4,5-DOPA-extradiol-dioxygenase from the best-known source of betalains-Beta vulgaris-after heterologous expression in Escherichia coli. The enzyme is a monomeric protein with a molecular mass of 32 kDa characterized by chromatography, electrophoresis and MALDI-TOF analysis. Enzyme kinetic properties are characterized in the production of betalamic acid, the structural, chromophoric and bioactive unit of plant pigment betalains.