Catalysis of three sequential dioxygenase reactions by thymine 7-hydroxylase

Liu, Chen-Kao; Hsu, Chin-An; Abbott, Mitchel T.

doi:10.1016/0003-9861(73)90443-8

Cited by 60 publications

(39 citation statements)

References 15 publications

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“…Similarly, the ratios of reaction rates of the three substrates with the N. crassa enzyme are estimated to be 4.6:2.3:1. 16 Thymine and HMU are bound at the same active site as shown by studies demonstrating that HMU competitively inhibits thymine hydroxylation with an observed K i that matches the K m for HMU utilization. 19,21 On the basis of the high K m and low k cat for FU , hydroxylation of this substrate by T7H is suggested to be physiologically irrelevant; the presence of an NAD-dependent FU dehydrogenase in N. crassa is consistent with this proposal.…”

Section: Pyrimidine and Purine Hydroxylases 21 Thymine 7-hydroxylasementioning

confidence: 89%

Section: Pyrimidine and Purine Hydroxylases 21 Thymine 7-hydroxylasementioning

confidence: 99%

“…[13][14][15][16] Each of these reactions requires Fe II , αKG, and O 2 and produces stoichiometric amounts of the respective primary product, CO 2 , and succinate. One atom of molecular oxygen is incorporated into succinate and the other into the primary products.…”

Section: Pyrimidine and Purine Hydroxylases 21 Thymine 7-hydroxylasementioning

confidence: 99%

“…Similarly, the ratios of reaction rates of the three substrates with the N. crassa enzyme are estimated to be 4.6:2.3:1. 16 Thymine and HMU are bound at the same active site as shown The reactivity of T7H with various thymine analogues nicely illustrates the remarkable chemical versatility associated with the Fe II /αKG family of enzymes. In addition to the three reactions shown above in Scheme 2, T7H oxidizes 5-vinyluracil, 5-methylthiouracil, 5,6-dihydrothymine, 1-methylthymine, 1-methyluracil, 1-ethyluracil, 6-azathymine, and others some of which are shown in Scheme 3.…”

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confidence: 99%

“…One atom of molecular oxygen is incorporated into succinate and the other into the primary products. [15][16][17] The Rhodotorula glutinis T7H sequence includes His 211, Asp 213, and His 268 as putative metal-binding ligands and Arg 284 as a likely αKG stabilizing residue, but no structural studies have been carried out to confirm these assignments.Efforts to characterize T7H have focused on the enzymes from fungi such as Neurospora crassa, R. glutinis, and Aspergillus nidulans that can grow on thymine as their sole nitrogen source. These microorganisms possess a salvage pathway enabling the host to utilize thymine as a pyrimidine source in the absence of the common "de novo" pathway of uracil biosynthesis (Fig.…”

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FeII/α-ketoglutarate hydroxylases involved in nucleobase, nucleoside, nucleotide, and chromatin metabolism

2008

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Fe II /α-ketoglutarate-dependent hydroxylases uniformly possess a double-stranded β-helix fold with two conserved histidines and one carboxylate coordinating their mononuclear ferrous ions. Oxidative decomposition of the α-keto acid is proposed to generate a ferryl-oxo intermediate capable of hydroxylating unactivated carbon atoms in a myriad of substrates. This perspective focuses on a subgroup of these enzymes that are involved in pyrimidine salvage, purine decomposition, nucleoside and nucleotide hydroxylation, DNA/RNA repair, and chromatin modification. The varied reaction schemes are presented, and selected structural and kinetic information is summarized. IntroductionFerrous ion and α-ketoglutarate (αKG)-dependent dioxygenases comprise an enzyme superfamily with members present in animals, plants, protists, fungi, bacteria and even viruses. Most representatives of this large group of enzymes couple the oxidative decarboxylation of αKG to various hydroxylation reactions ( Fig. 1), but others are capable of catalyzing desaturation, epoxidation, halogenation, ring formation, or ring expansion reactions, which allows them to fill a wide variety of biological roles including antibiotic biosynthesis, hypoxic sensing, DNA repair, and various types of metabolite transformations. [1][2][3] Not surprisingly, the primary substrates also are diverse and include proteins, lipids, nucleic acids, and a myriad of small molecules that can be used for synthesis or undergo degradation.The sequences of Fe II /αKG dioxygenases show little overall identity, yet the diverse reactions all are catalyzed by proteins with the same core fold and use similar chemistries. 4 The hallmark of these enzymes is their use of Fe II to activate molecular oxygen according to a mechanism (Scheme 1) first proposed by Hanauske-Abel and Günzler in 1982 for prolyl 4-hydroxylase. 5 (A) In the absence of substrates, a "facial triad" (usually two His plus one Asp or Glu occurring in a His-X-Asp/Glu-X n -His motif) weakly bind one face of the hexacoordinate metal. 6,7 (B) The αKG co-substrate displaces two waters and coordinates Fe II in a bidentate fashion with its C1 carboxyl and C2 keto oxygens. The binding of αKG is Correspondence to: Robert P. Hausinger, hausinge@msu.edu. NIH Public Access Author ManuscriptDalton Trans. Author manuscript; available in PMC 2010 July 20. This perspective focuses on the modification of nucleobases, nucleosides, nucleotides, and chromatin by the Fe II and αKG dependent hydroxylases (Table 1). We discuss the degradation and salvage of free bases by the fungal enzymes thymine 7-hydroxylase and xanthine hydroxylase. Next, nucleoside hydroxylases are briefly described. We then examine the developmental modification of DNA in kinetoplastid protozoans and summarize evidence that the JBP1 and JBP2 proteins possess thymidine hydroxylase activity. The oxidative repair of DNA by Escherichia coli AlkB is discussed, and the properties of mammalian homologues are summarized. Finally, we present emerging evidence pointing to...

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Section: Pyrimidine and Purine Hydroxylases 21 Thymine 7-hydroxylasementioning

confidence: 89%

Section: Pyrimidine and Purine Hydroxylases 21 Thymine 7-hydroxylasementioning

confidence: 99%

Section: Pyrimidine and Purine Hydroxylases 21 Thymine 7-hydroxylasementioning

confidence: 99%

“…Similarly, the ratios of reaction rates of the three substrates with the N. crassa enzyme are estimated to be 4.6:2.3:1. 16 Thymine and HMU are bound at the same active site as shown The reactivity of T7H with various thymine analogues nicely illustrates the remarkable chemical versatility associated with the Fe II /αKG family of enzymes. In addition to the three reactions shown above in Scheme 2, T7H oxidizes 5-vinyluracil, 5-methylthiouracil, 5,6-dihydrothymine, 1-methylthymine, 1-methyluracil, 1-ethyluracil, 6-azathymine, and others some of which are shown in Scheme 3.…”

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confidence: 99%

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