PMID:18817418

Citation	Panay, AJ and Fitzpatrick, PF (2008) Kinetic isotope effects on aromatic and benzylic hydroxylation by Chromobacterium violaceum phenylalanine hydroxylase as probes of chemical mechanism and reactivity. Biochemistry 47:11118-24
Abstract	Phenylalanine hydroxylase from Chromobacterium violaceum (CvPheH) is a non-heme iron monooxygenase that catalyzes the hydroxylation of phenylalanine to tyrosine. In this study, we used deuterium kinetic isotope effects to probe the chemical mechanisms of aromatic and benzylic hydroxylation to compare the reactivities of bacterial and eukaryotic aromatic amino acid hydroxylases. The (D) k cat value for the reaction of CvPheH with [(2)H 5]phenylalanine is 1.2 with 6-methyltetrahydropterin and 1.4 with 6,7-dimethyltetrahydropterin. With the mutant enzyme I234D, the (D) k cat value decreases to 0.9 with the latter pterin; this is likely to be the intrinsic effect for addition of oxygen to the amino acid. The isotope effect on the subsequent tautomerization of a dienone intermediate was determined to be 5.1 by measuring the retention of deuterium in tyrosine produced from partially deuterated phenylalanine; this large isotope effect is responsible for the normal effect on k cat. The isotope effect for hydroxylation of the methyl group of 4-CH 3-phenylalanine, obtained from the partitioning of benzylic and aromatic hydroxylation products, is 10. The temperature dependence of this isotope effect establishes the contribution of hydrogen tunneling to benzylic hydroxylation by this enzyme. The results presented here provide evidence that the reactivities of the prokaryotic and eukaryotic hydroxylases are similar and further define the reactivity of the iron center for the family of aromatic amino acid hydroxylases.
Links	PubMed PMC2603180 Online version:10.1021/bi801295w
Keywords	Chromobacterium/enzymology; Hydroxylation; Isotopes; Kinetics; Models, Chemical; Phenylalanine Hydroxylase/chemistry; Phenylalanine Hydroxylase/metabolism; Recombinant Proteins/chemistry; Recombinant Proteins/metabolism; Substrate Specificity; Thermodynamics
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
CHRVO:PH4H		GO:0004505: phenylalanine 4-monooxygenase activity	ECO:0000314:		F		Fig. 1 Phenylalanine hydroxylase catalytic activity increases as DTT concentration increases.	complete CACAO 6683
CHRVO:PH4H	enables	GO:0004505: phenylalanine 4-monooxygenase activity	ECO:0000314: direct assay evidence used in manual assertion		F		Seeded From UniProt	complete

References

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