Metabolic fate of 3,4-dihydroxyphenylpyruvic acid(DHPP) in rats. I. Specific transformation of DHPP to L-3,4-dihydroxyphenylalanine in vitro.

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Abstract
3,4-Dihydroxyphenylpyruvic acid-2-14C (DHPP-2-14C) was prepared from glycine-2-14C and the specific formation of L-3,4-dihydroxyphenylalanine (L-dopa) from DHPP was shown in vitro. The metabolism of L-dopa-3-14C was also investigated in vitro for comparison. In rat brain and small intestinal homogenates, L-dopa was formed gradually as the main metabolite from DHPP-2-14C but dopamine and its metabolites were very slight amount. On the contrary, dopamine was detected dominantly from L-dopa-3-14C in small intestinal homogenates. In the liver and kidney homogenates, DHPP was metabolized extensively and disappeared immediately with concomitant rapid formation of L-dopa. Dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) were detected subsequently as the main metabolite. The same extensive metabolism of L-dopa-3-14C was also shown in the liver homogenates. Formation of L-dopa from DHPP was identified by TLC and reverse isotope dilution method. L-Phenylalanine, L-tyrosine, L-tryptophan and L-glutamate were revealed to be effective amino donors to DHPP. The aromatic L-amino acids were particularly effective but D-phenylalanine showed little activity. The liberation of 14CO2 from DHPP-2-14C was also recognized in vitro. The 14CO2 liberating activity from DHPP-2-14C located in 105,000 g supernatant soluble fraction in the liver and kidney wherein the activity in the liver was about 4 fold higher than that in the kidney. The activity was inhibited by sodium azide, sodium diethyldithiocarbamate, p-hydroxyphenylpyruvate and phenylpyruvate but not influenced by SKF 525A [.alpha.-phenyl-.alpha.-propylbenzene acetic acid, 2-(diethylamino)ethyl ester hydrochloride], carbon monoxide, EDTA, .alpha.,.alpha.''-dipyridyl and pyruvate. Methylene blue, dichlorphenolindophenol and ascorbate was activated about 2 to 3 fold.