Xci . the Reversible Enzymic Oxidation of Vitamin C

SOME years ago during the progress of an inquiry on the production of an antiscorbutically active cider from Bramley's Seedling apples it was observed that the juice expressed from the fruit while retaining a very high proportion of its antiscorbutic activity did not reduce indophenol. At that time the writer held the view that the capacity for reducing this indicator was mainly due to a substance which, although closely associated with the vitamin in a protective way, was not the active principle itself. The probability of the production of a reversibly oxidised active form of the vitamin was not at that time seriously considered by him. This problem was reinvestigated recently in view of the fact which has now been established that 1-ascorbic acid possesses antiscorbutic activity per se and that when this compound is reversibly oxidised [Szent-Gy6rgyi, 1928] it retains its activity [Tillmans et al., 1932; Hirst and Zilva, 1933]. It was found again that juice expressed from Bramley's Seedling apples although unable to reduce indophenol was antiscorbutically active. Thus a daily dose of 3 ml. of the non-reducing apple juice afforded protection to guinea-pigs equivalent to 0*25-0*5 mg. of ascorbic acid or to rather less than 1 ml. of decitrated lemon juice (10 i.u.). This potency is not very much less than that obtained with intact tissue of these apples (usually about 15 i.u. per 3 g.). The apple juice, it was further found, reduced indophenol immediately after expression but rapidly lost this power of reduction. Aqueous extracts prepared with or without cyanide, unlike alcoholic, trichloroacetic acid and strongly acid extracts did not reduce indophenol. Furthermore, the non-reducing apple juice after treatment with hydrogen sulphide regained the property of reducing indophenol. This evidence is very suggestive of a case of enzymic reversible oxidation. Experiments will here be described which strongly support this hypothesis.