Metabolism of ascorbic acid

Whilst these acids are of minor importance in man, another multifunctional acid, ascorbic add (vitamin C 6), has an apparent role in human iron metabolism as one of the postulated factors aiding iron uptake. Ascorbic add reduces Fe111 to Fe" with probable complexation of the latter. It thus converts Fe"1 to a more soluble form. Ascorbic acid can also reduce Cu" to Cu1 (equation 1), and there is accumulating evidence of a link between the metabolism of ascorbic acid and that of Cu.34... 

Loewus FA (1999) Biosynthesis and metabolism of ascorbic acid in plants and of analogs of ascorbic acid in fungi. Phytochemistry 52, 193-210. 

The metabolism of ascorbic acid has yet to be clarified. Only one of the major water-soluble urinary metabolites of ascorbic acid has been isolated and characterized the others and the matabolic pathways involved are yet to be defined. When these pathways and their intermediates are understood, there will be good possibilities for significant nutritional and medical innovation. 

Metabolism of ascorbic acid can lead to deposition of oxalate crystals in kidney tissue. Reduction of carcinogenic Cr(VI) by ascorbic acid generates as-corbate-Cr(III)-DNA cross-links that have been linked to mutagenicity and the formation of DNA lesions. Uranyl acetate-ascorbate has also been shown to nick plasmid DNA. 

The significance of adrenolutin in schizophrenic urine is still debated,28 and other unusual indoles in the urine of mentally retarded patients have been detected.2 A very high rate (10 x normal) of metabolism of ascorbic acid by schizophrenics has led Van der KampS to administer high doses therapeutically. 

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. 

Studies of plasma levels have also demonstrated statistically some differences in distribution and possibly in metabolism of ascorbic acid of the sort which would be expected on biochemical grounds to occur in dif-... 

More detailed accounts of particular enzyme reactions in the metabolism of ascorbic acid have appeared (K. Suzuki, Y. Mano, and N. Shimazono, Enzymatic formation of L-gulonolactone from n-glucuronolactone by rat liver microsomes. J. Biochem. (Tokyo) 47, 846-849, 1960 K. Suzuki, Y. Mano, and N. Shimazono, Conversion of L-gulonolactone to L-ascorbic acid. Properties of the microsomal enzyme in rat liver. J. Biochem. (Tokyo) 48, 313-315, 1960 J. D. Smiley, and G. Ashwell, Purification and properties of fi-L-hydroxy acid dehydrogenase. II. Isolation of fi-keto-L-gulonic acid, an intermediate in L-xyliJose biosynthesis. J. Biol. Chem. 236, 357-364, 1961). 

In the investigation of vitamin deficiencies, it is well to bear in mind that diets deficient in a rangle vitamin produce metabolic disorders which alter the animal s requirement for other nutritional factors. Where pantothenic acid deficiency is concerned, there is evidence that the metabolism of ascorbic acid, biotin, protein, carbohydrate, and fat are involved. 

Mental symptoms (depression) accompany the physical symptoms of vitamin-C deficiency disease (scurvy). In 1957, Akerfeldt reported that the serum of schizophrenics had been found to have greater power of oxidizing N,N-dimethyl-p-phenylenediamine than that of other persons. Several investigators then reported that this difference is due to a smaller concentration of ascorbic acid in the serum of schizophrenics than of other persons. This difference has been attributed to the poor diet and increased tendency to chronic infectious disease of the patients (Benjamin, 1958 Kety, 1959), and has also been interpreted as showing an increased rate of metabolism of ascorbic acid by the patients (Hoffer and Osmond, 1960 Briggs, 1962). It is my opinion, from the study of the literature, that many schizophrenics have an increased metabolism of ascorbic acid, presumably genetic in origin, and that the... 

Pietronigro, D. D., Hovsepian, M., Demipoulos, H. B. and Flamm, E. S., 1985, Reductive metabolism of ascorbic acid in the central nervous system. Brain Res. 333 161-164. 

The main source of carbon dioxide is the C-1 atom of the ascorbic acid molecule, whereas the C atoms 1 and 2 represent the basic structure for oxalic acid. The formation of oxalic acid with excessive supplies of ascorbic acid has been used as one argument against pharmacological doses, especially for persons who are sensitive to the development of a nephrolithiasis. The human daily excretion amounts to 30-40 mg oxalic acid and originates 35-50% from the metabolism of ascorbic acid and 50-65% from glycine and glyoxalic acid. The additional supply of 1-9 g ascorbic acid per day led to an increase of the normal excretion of oxalic acid by 0.0-68.0 mg/day (Moser et al., 1982). Normal persons without any metabolic disease are therefore not seriously affected in their oxalic acid excretion by single excessive doses of ascorbic acid. 

---