Betacyanin decolourizing enzyme in Amaranthus tricolor seedlings

The characterization and partial purification of an enzyme from Amaranthus tricolor which decolourizes betacyanin are described. The enzyme occurs in greatest amounts in the roots and in 3.5-4-day-old seedings. Preparation from an acetone powder of roots results in a more active and more stable enzyme than that obtained from crude buffer extraction. The activity is in the 130 000 g supernatant from sucrose-buffer extraction. It has a pH optimum of 3.4 K_m towards amaranthin of 3.1 × 10^?6 M and towards betanin of 3.5 × 10^?6 M, and is inhibited by lack of oxygen, and by azide, diethyldithiocarbamate, thiourea, dithiothreitol and cysteine. The product of the reaction has the spectral and electrophoretic properties of betalamic acid. The possibility of enzymic decolourization of betacyanin during acetic acid extraction used for assay of the pigment in the Amaranthus bioassay for cytokinins needs to be recognized.