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 glyoxylate 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.