On the catalytic mechanism of tryptophan hydroxylase

Graham R. Moran, Agnes Derecskei-Kovacs, Patrick J. Hillas, Paul F Fitzpatrick

Research output: Contribution to journalArticle

47 Citations (Scopus)

Abstract

Tryptophan hydroxylase catalyzes the hydroxylation of tryptophan using tetrahydrobiopterin and molecular oxygen. With tyrosine as a substrate, the amount of C4a-hydroxypterin formed greatly exceeds the amount of dihydroxyphenylalanine formed, consistent with oxygen-oxygen bond cleavage occurring in a step prior to amino acid hydroxylation. With L-indole-2H5- tryptophan, L-4-2H- or L-5-2H-tryptophan as substrate there is no isotope effect on the V/K value for tryptophan. There is an inverse isotope effect on the V(max) value with L-indole-2H5-tryptophan and L-5-2H-tryptophan, but no effect with L-4-2H-tryptophan. Comparison of the measured isotope effects with values of calculated secondary equilibrium isotope effects for tryptophan hydroxylation indicate that the results are most consistent with the formation of a cationic species. Retention of the isotopic label from L- 5-2H-tryptophan in the product confirms that an NIH shift occurs in tryptophan hydroxylase and shows that the direction of shift is from carbon 5 to carbon 4. The degree of retention of the deuterium is higher when the deuterium is initially on carbon 4 rather than carbon 5.

Original languageEnglish (US)
Pages (from-to)4535-4541
Number of pages7
JournalJournal of the American Chemical Society
Volume122
Issue number19
DOIs
StatePublished - May 17 2000
Externally publishedYes

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Tryptophan Hydroxylase
Tryptophan
Hydroxylation
Isotopes
Carbon
Deuterium
Oxygen
Molecular oxygen
Substrates
Amino acids
Labels
Dihydroxyphenylalanine
Tyrosine
Amino Acids

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

On the catalytic mechanism of tryptophan hydroxylase. / Moran, Graham R.; Derecskei-Kovacs, Agnes; Hillas, Patrick J.; Fitzpatrick, Paul F.

In: Journal of the American Chemical Society, Vol. 122, No. 19, 17.05.2000, p. 4535-4541.

Research output: Contribution to journalArticle

Moran, Graham R. ; Derecskei-Kovacs, Agnes ; Hillas, Patrick J. ; Fitzpatrick, Paul F. / On the catalytic mechanism of tryptophan hydroxylase. In: Journal of the American Chemical Society. 2000 ; Vol. 122, No. 19. pp. 4535-4541.
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