The oxidation of <i>l</i>-ascorbic acid by plant enzymes

Abstract

THAT ascorbic acid can be dehydrogenated by an aerobic oxidase present in the apple has been shown by one of us [Zilva, 1934].It was further found that this enzyme is also capable of dehydrogenating another member of the ascorbic acid series, namely d-gluco-ascorbic acid (d-3-ketoglucoheptonofuranolactone), which does not possess antiscorbutic activity even in high doses [Zilva, 1935; 1936].Stereochemical structure and biological activity of these compounds are there- fore not determining factors in this enzymic oxidation.The apple, however, is not the only plant containing an aerobic enzyme which oxidizes ascorbic acid reversibly.Szent-Gyorgyi [1930; 1931] established the presence of one in cabbage (Brassica oleracea L.), Tauber et al. [1935] in Hubbard squash (Cucurbita maxima), Hopkins & Morgan [1936] in cauliflower, Srinivasan [1936] in the pods of the drumstick tree [Moringa pterygosperma), Barron et al. [1936] in lettuce, peach and watercress, and Kertesz et al. [1936] in pumpkin, pea, string bean, Lima bean, sweet corn, Swiss chard, carrots, parsnips and spinach.The present investigation deals with a comparative study of the enzymic reversible oxidation of ascorbic acid by the cabbage, cauliflower, cucumber, marrow, apple and potato.All the experiments were carried out under stan- dardized conditions in order to ascertain whether the enzymes or systems of enzymes involved in the oxidation are identical.EXPERIMENTAL