The non-specificity of the ascorbic acid oxidase

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Abstract
Dialysed cucumber juice, apart from its ability to oxidize the ascorbic acid analogues directly, also oxidized reductone and reductic acid. In the compounds containing the 5-membered ring, the O2 uptake agreed with the values calculated from the disappearance of the substrate; in the case of reductone the O2 uptake was less than that calculated. It was suggested that some of the substrate was utilized in a side reaction. Low concentrations of 1-ascorbic acid were much more readily oxidized by dialysed juice than d-gluco-ascorbic acid, reductic acid and reductone, indicating a greater affinity of the enzyme for the naturally occurring vit. Undialysed, but not dialysed, juice oxidized dihydroxymaleic acid. Dialysed juice, however, regained its oxidizing activity towards this substrate on addition of catechol or phenol. In the oxidation of dihydroxymaleic acid there was a formation of CO2 and a higher O2 uptake than that calculated from the disappearance of the substrate. The possible mechanism involved in this more complete degradation of the substrate was discussed. Dialysed cucumber juice was capable of oxidizing glutathione and cysteine. The enzyme responsible for this oxidation was not identical with the ascorbic acid oxidase present in the juice, since the relative rates of oxidation of the sulphydryl compounds and of ascorbic acid varied with different samples of dialysed juice.