ALTHOUGH ascorbic acid oxidase is regarded as a copper enzyme, thiourea has not been reported as an inhibitor of it. Previous reports, in fact, point out a lack of inhibition of the oxidase by thiourea1,2, although phenol thiourea has been stated to be inhibitor3,4. During a study of the ascorbic acid oxidase of germinating lettuce seed, thiourea inhibition of the oxidase has been observed. Extracts of lettuce seeds were prepared and tested for ascorbic acid oxidase activity by means of conventional Warburg techniques. Direct titration of ascorbic acid was ruled out as thiourea interferes in the titration.
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MAYER, A. Inhibition of Ascorbic Acid Oxidase by Thiourea. Nature 180, 1417–1418 (1957). https://doi.org/10.1038/1801417b0
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