Formation of malonaldehyde in vitamin E deficiency and its relation to the inhibition of gulonolactone oxidase.

The impairment of synthesis in vitro of ascorbic acid by liver extracts from animals deprived of vitamin E (1, 2) is due to the inhibition of the enzyme(s) located in the microsomes (3) which catalyzes the oxidation of n-gulonolactone to L-ascorbic acid. This enzyme or enzymic complex will be termed gulonolactone oxidase. Concurrent with the inhibition of gulonolactone oxidase, a material is formed which reacts with thiobarbituric acid to produce a red pigment, and because all of the factors which restored the synthesis of ascorbic acid also stopped the formation of the TBA-reacting material, the hypothesis was advanced that both phenomena were related (4). The inhibition of ascorbic acid synthesis in vitro is apparent 24 hours after starting the animals on a low tocopherol diet. The appearance of this manifestation before any other symptom of vitamin E deficiency led to the search for some condition inherent to the test system which might enhance the inhibition. This paper reports the existence in the test system for ascorbic acid synthesis of several processes which result in the formation of TBAl-reacting material. These involve spontaneous, catalytic, but nonenzymic, as well as enzymic processes. The results also show that at least two TBA-reacting materials are produced; the most abundant appears to be malonaldehyde, which has been implicated by Patton et al. (5, 6) as a TBAreacting material resulting from lipid peroxidation. Gulonolactone oxidase has been obtained in a soluble form from rat liver microsomes, and further fractionated to allow a more detailed study of the interference in ascorbic acid synthesis by malonaldehyde formation.