Stuaies on the Relationship between L-Ascorbic Acid and o-Diphenol Oxidase Activity in the Radish (Raphanus Safivus L.)

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The effect of L-ascorbic acid on o-diphenol oxidase activity in the radish was studied. The total concentration of L-ascorbic acid and dehydroascorbic acid was not different so much on various portion in the radish (27.5-30.5mg%) and L-ascorbic acid accounted for about 1/2 part of total content in the juice of grated radish, and it was found only a little in cell-residue. L-Ascorbic acid inhibited odiphenol oxidase activity in fresh tissue of radish. o-Diphenol oxidase in the radish was purified by ammonium sulfate fractionation and gel filtration by Sephadex G-25. The purified enzyme preparation appears a single peak in acrylamide electrophoresis. The enzyme displayed the highest activity at pH 8.3 using dopa as substrate. The activity of o-diphenol oxidase was inhibited with L-ascorbic acid, cysteine, glutathione as the reducing agent and KCN, and activated by Cu<SUP>++</SUP>. It was suggested that the inhibition of o-diphenol oxidase with L-ascorbic acid was due to reduction of enzymic product.
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