The pathways of oxalate formation from phenylalanine,tyrosine, tryptophan and ascorbic acid in the rat

The metabolic pathway by which L-¹⁴C₁]phenylalanine, L-¹⁴C₁]tyrosine, L-¹⁴C₁]tryptophan, and L-¹⁴C₁]ascorbic acid are converted to ¹⁴C]oxalate have been investigated in the male rate. Only ¹⁴C]oxalate was detected in the urine of rats injected with L-¹⁴C₁]ascorbic acid, but ¹⁴C]-labeled oxalate, glycolate, glyoxylate, glycolaldehyde, glycine, and serine were recovered from the ¹⁴C₁]-labeled aromatic amino acids. DL-Phenyllactate, an inhibitor of glycolic acid oxidase and glycolic acid dehydrogenase, reduced the amount of ¹⁴C]oxalate recovered in the urine of rats given the ¹⁴C₁]-labeled aromatic amino acids, but increased the amount of ¹⁴C]glycolate formed from L-¹⁴C₁]-phenylalanine and L-¹⁴C₁]tyrosine and the amount of ¹⁴C]glycolate produced from ¹⁴C₁]tryptophan. Based on the ¹⁴C]labeled intermediates identified and the relative distribution of the radioactivity, it is postulated that phenylalanine and tyrosine are converted to oxalate via glycolate which is oxidized directly to oxalate by glycolic acid dehydrogenase. Tryptophan is metabolized via glyxylate which is oxidized directly to oxalate by glycolic acid oxidase. Neither glycolate, glyoxylate, glycolic acid oxidase or glycolic acid dehydrogenase are involved in the formation of oxalate from ascorbic acid.