Studies on phenylalanine and tyrosine hydroxylation by rat brain tyrosine hydroxylase

Ira Katz, Thomas Lloyd, Seymour Kaufman

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Tyrosine hydroxylase (EC, presumably the rate-limiting enzyme in the biosynthesis of catecholamines, is known to catalyze the hydroxylation of both phenylalanine and tyrosine. Using both an isolated enzyme preparation and a synaptosomal preparation, where some architectural integrity of the tissue has been preserved, we have attempted to evaluate the manner in which these two substrates are hydroxylated by rat brain tyrosine hydroxylase. In the presence of tetrahydrobiopterin the isolated enzyme catalyzes the hydroxylation of phenylalanine to 3,4-dihydroxyphenylalanine with the release of free tyrosine as an obligatory intermediate. In contrast, the rat brain striatal synaptosomal preparation in the presence of endogenous cofactor converts phenylalanine to 3,4-dihydroxyphenylalanine without the release of free tyrosine.

Original languageEnglish (US)
Pages (from-to)567-578
Number of pages12
JournalBBA - Enzymology
Issue number3
Publication statusPublished - Oct 11 1976


All Science Journal Classification (ASJC) codes

  • Medicine(all)

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