CHARACTERIZATION OF A S-ADENOSYL-L-METHIONINE - ERIODICTYOL 4'-O-METHYLTRANSFERASE FROM CITRUS AURANTIUM - DEVELOPMENTAL CHANGES IN THE LEVELS OF 4'-O-METHOXYFLAVONOIDS AND S-ADENOSYL-L-METHIONINE - ERIODICTYOL 4'-O-METHYLTRANSFERASE ACTIVITY

摘要

A S-adenosyl-L-methionine :eriodictyol 4'-O-methyltransferase (4' - OMT) was partially purified from Citrus aurantium by precipitation with ammonium sulfate and gel permeation chromatography. The molecular mass of the OMT was estimated to 52 kDa. The optimum pH was about 7.5. The enzyme was activated by Mg2+ and by EDTA. The activation by Mg2+ is saturable with a Ka of 18 mu M. The Km for eriodictyol and S-adenosylmethionine were 141 and 86 mu M, respectively. S-adenosyl-L-homocysteine inhibits the methylation of eriodictyol by S-adenosyl-L-methionine. This inhibition is non competitive for eriodictyol and S-adenosyl-L-methionine. Furthermore, the evolution of 4'-OMT activity during the development of leaves, flower buds and fruits of C. aurantium was studied and compared with the accumulation of total and 4'-methoxyflavonoids. [References: 27]