Open AccessPurification and properties of a new S ‐adenosyl‐ l ‐ methionine:flavonoid 4′‐ O ‐methyltransferase from carnation ( Dianthus caryophyllus L.)
Author(s) -
Curir Paolo,
Lanzotti Virginia,
Dolci Marcello,
Dolci Paola,
Pasini Carlo,
Tollin Gordon
Publication year - 2003
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1033.2003.03729.x
Subject(s) - carnation , chemistry , enzyme , flavonoid , dianthus , biochemistry , o methyltransferase , stereochemistry , methionine , kaempferol , enzyme assay , methyltransferase , biology , methylation , botany , dna , amino acid , antioxidant
A new enzyme, S ‐adenosyl‐ l ‐methionine:flavonoid 4′‐ O ‐methyltransferase (EC 2.1.1.‐) (F 4′‐OMT), has been purified 1 399‐fold from the tissues of carnation ( Dianthus caryophyllus L). The enzyme, with a molecular mass of 43–45 kDa and a pI of 4.15, specifically methylates the hydroxy substituent in 4′‐position of the flavones, flavanones and isoflavones in the presence of S ‐adenosyl‐ l ‐methionine. A high affinity for the flavone kaempferol was observed ( K m = 1.7 µ m ; V max = 95.2 µmol·min −1 ·mg −1 ), while other 4′‐hydroxylated flavonoids proved likewise to be suitable substrates. Enzyme activity had no apparent Mg ++ requirement but was inhibited by SH‐group reagents. The optimum pH value for F 4′‐OMT activity was found to be around neutrality. Kinetic analysis of the enzyme bi‐substrate reaction indicates a Ping‐Pong mechanism and excludes the formation of a ternary complex. The F 4′‐OMT activity was increased, in both in vitro and in vivo carnation tissues, by the inoculation with Fusarium oxysporum f. sp. dianthi . The enzyme did not display activity towards hydroxycinnamic acid derivatives, some of which are involved, as methylated monolignols, in lignin biosynthesis; the role of this enzyme could be therefore mainly defensive, rather than structural, although its precise function still needs to be ascertained.