TYROSINE METABOLISM IN RATS: p-HYDROXYPHENYLACETIC ACID IS SYNTHESIZED VIA p-HYDROXYPHENYLPYRUVIC ACID

Deuterium-labelled p-hydroxyphenylpyruvic acid (PHPPA) was synthesized, and injected intraperitoneally to rats. Deuterium-labelled metabolites excreted into urine were analyzed by means of gas chromatography-negative ion chemical ionization mass spectrometry. During four hours after the injection, the ratio of deuterium-labelled p-hydroxyphenylacetic acid (PHPA) to non-deuterated one reached a high level. On the other hand, the ratio of labelled p-tyramine to non-labelled one remained at a low level. These results indicate that PHPA is biosynthesized not only through deamination of p-tyramine but also through oxidative decarboxylation of PHPPA.