Biosynthesis and Degradation of Ascorbic Acid in Animals

The most important recent addition to our knowledge of ascorbic acid is the series of stepwise enzyme reactions by which it is made in animal tissues and through which it is related to the reactions of other carbohydrates in the body. The biosynthetic pathways of ascorbic acid in plants have been partially elucidated, but less successfully, since it appears that two different pathways may operate (L21). These important advances have been the subject of a number of reviews (M7, B38, B39, K5). 

A recent study (Tl) showed that in Penicillium notatum, n-glucose-was converted to n-araboascorbic acid with 80 % of the activity in carbon 1, showing the possibility of formation of D-araboascorbic acid from D-glucose without rupture and inversion of the carbon chain. 

The possibility that the biosynthesis of ascorbic acid occurred through sorbose and 2-keto-L-gulonic acid, as in the chemical synthesis, was eliminated when the latter was not converted to ascorbic acid, and L-sorbose-6-C gave rise to ascorbic acid labeled in both carbons 1 and 6. Sorbose was evidently degraded and converted to glucose before being transformed into ascorbic acid. 

IMagram of the glucuronic acid pathway ot glucose metabolism. 

The new knowledge of ascorbic acid biosynthesis and degradation has called attention to the variable metabolism of ascorbic acid, induced by drugs of various kinds, and to the complementary effects on the metabolism of drugs, produced by ascorbic acid. Changes of this sort may eventually explain many puzzling features of the metabolism of ascorbic acid in scorbutic animals in different physiological states. 

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