PMID: 3769914Oct 1, 1986Paper

Stereoselective effects in the interactions of pterin cofactors with rat-liver phenylalanine 4-monooxygenase

European Journal of Biochemistry
J HaavikT Flatmark

Abstract

The (6R) and (6S) epimers of l-erythro-tetrahydrobiopterin (BH4) and some of its structural analogs, were tested as cofactors and non-covalent effectors in the phenylalanine 4-monooxygenase (phenylalanine hydroxylase, EC 1.14.16.1) reaction. The oxidation-reduction potentials (Em,7) of the free (not enzyme-bound) form of the (6R) and (6S) epimers were rather similar (range 174-184 mV) for the oxidation of tetrahydropterins to quinonoid dihydropterins. Rapid-mixing kinetic experiments were performed at 20 degrees C under conditions which allow only a few turnover reactions of the enzyme. Three main oxidation products were identified spectroscopically at pH 6.8 for all three tetrahydropterins tested: the C(4a)-hydroxy derivatives, the quinonoid dihydropterins, and the stable 7,8-dihydropterins (in that sequence). The formation of the C(4a)-hydroxy forms closely paralleled that of tyrosine, and supports the proposal that this covalent adduct is formed as an immediate product on completion of the catalytic cycle. Assay of the initial rate of C(4a)-hydroxy derivative formation represents a new approach in kinetic studies of this enzyme, and the kinetic parameters obtained for the phenylalanine-activated enzyme are presented. The aff...Continue Reading

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Citations

Nov 1, 1992·Comparative Biochemistry and Physiology. B, Comparative Biochemistry·Y BelJ Ferré
Apr 30, 2014·Photochemistry and Photobiology·Andrey A BuglakMikhail S Kritsky
Jun 1, 1997·Protein Science : a Publication of the Protein Society·B KobeB E Kemp
May 15, 2003·Journal of Biomolecular Structure & Dynamics·Knut Teigen, Aurora Martinez
Aug 29, 2006·FASEB Journal : Official Publication of the Federation of American Societies for Experimental Biology·Angel L PeyKarin U Schallreuter
May 24, 2019·Proceedings of the National Academy of Sciences of the United States of America·Marte Innselset FlydalJuan A Hermoso
Dec 8, 2020·Free Radical Research·Andrey A BuglakMikhail S Kritsky
Jan 15, 1992·Biochemical and Biophysical Research Communications·A MartínezT Flatmark
Oct 21, 2004·Journal of the American Chemical Society·Angel Luis PeyAurora Martínez

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