The interconversion of the 5,6,7,8-tetrahydro-, 6,7,8-dihydro-, and radical forms of 6,6,7,7-tetramethyldihydropterin. A model for the biopterin center of aromatic amino acid mixed function oxidases

Eberlein, Gert; Bruice, Thomas C.; Lazarus, Robert A.; Henrie, Robert N.; Benkovic, Stephen J.

doi:10.1021/ja00337a047

Cited by 61 publications

(71 citation statements)

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“…Our reinvestigation of the autoxidation of H4B presented here basically confirm earlier studies with respect to product formation (22), oxygen consumption (7,10), nitric oxide consumption (16), kinetics (14,16), and inhibitory effect of SOD (6,15,16). Beyond this, our ESR spin trapping experiments for the first time unequivocally prove that tetrahydrobiopterin reacts at physiological pH with molecular oxygen to produce free O 2 .…”

Section: Discussionsupporting

confidence: 89%

“…In this context, also a disagreement exists in the literature (11,12) whether superoxide is formed by reaction 4. From their examination of the autoxidation of H4B models, methylated tetra-and dihydropterins, Bruice and coworkers (14) proposed that in the initial, rate-controlling electron-transfer step a (H4B . (18) it was referred to as a "superoxide scavenger."…”

Section: Tetrahydrobiopterin (H4b)mentioning

confidence: 99%

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The Autoxidation of Tetrahydrobiopterin Revisited

Kirsch

Korth

Stenert

et al. 2003

Journal of Biological Chemistry

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It has been known for quite some time that tetrahydrobiopterin (H4B) is prone to autoxidation in the presence of molecular oxygen. Evidence has been presented that in this process superoxide radicals may be released, although their intermediacy never has been directly proven. In the present study, the autoxidation of H4B was reinvestigated with the aim to find direct evidence for superoxide formation. By means of two specific assays, namely elicitation of luminescence from lucigenin and ESR-spectrometric detection of the DEPMPO-OOH radical adduct, the release of free superoxide radicals was unequivocally demonstrated. The production of superoxide radicals was further corroborated by interaction with nitric oxide. The kinetics of the autoxidation process was established. Our data fully confirm earlier conclusions that the direct reaction between H4B and oxygen serves as an initiation reaction for the further, rapid reaction of the thus formed superoxide with H4B, thereby very likely establishing a chain reaction process involving reduction of molecular oxygen by the intermediary tetrahydrobiopterin radical. Conclusively, because H4B can per se induce oxidative stress, an in vivo overproduction of this pterin, as is evident in various diseases, may be responsible for the observed acceleration of pathophysiological pathways.

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Section: Discussionsupporting

confidence: 89%

Section: Tetrahydrobiopterin (H4b)mentioning

confidence: 99%

The Autoxidation of Tetrahydrobiopterin Revisited

Kirsch

Korth

Stenert

et al. 2003

Journal of Biological Chemistry

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“…Anaerobic solutions of 1 mM BH 4 and DTT (3 mM final concentration) were added to the protein containing arginine when BH 4 -repleted samples were needed. The concentration of BH 4 was determined by its absorbance at 298 nm (⑀ 298 ϭ 9.4 ϫ 10 3 M Ϫ1 cm Ϫ1 ) measured in the HEPES buffer at pH ϭ 7.5 and found to be similar to the reported value (22). The solution was then incubated overnight on ice to allow completeness of the equilibration.…”

Section: Methodsmentioning

confidence: 70%

Dynamic Regulation of the Inducible Nitric-oxide Synthase by NO

Gautier

Négrerie

Wang

et al. 2004

Journal of Biological Chemistry

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We studied by ultrafast time-resolved absorption spectroscopy the geminate recombination of NO to the oxygenase domain of the inducible NO synthase, iNOSoxy, and to mutated proteins at position Trp-457. This tryptophan interacts with the tetrahydrobiopterin cofactor BH 4 , and W457A/F mutations largely reduced the catalytic formation of NO. BH 4 decreases the rate of NO rebinding to the ferric iNOSoxy compared with that measured in its absence. The pterin has a larger effect on W457A/F than on the WT protein by increasing NO release from the protein. Therefore, BH 4 raises the energy barrier for NO recombination to the mutated proteins in contrast with our observations on eNOS (SlamaSchwok, A., Né grerie, M., Berka, V., Lambry, J. The inducible NO-synthase (iNOS), 1 best characterized from macrophages, generates the highest NO concentration among the three isoforms of NOS. High NO concentrations counter pathogens by their cytotoxicity and taking part in the response of the immune system. In contrast, the constitutive isoforms, the neuronal nNOS and, especially, the endothelial eNOS produce NO at low concentrations, which acts as a physiological signal in vasorelaxation, neurotransmission, and oxygen detection (1).The NOS enzymes utilize NADPH as a donor of electrons, arginine, and oxygen as co-substrates (2). The cofactor tetrahydrobiopterin BH 4 is required for NO production and strongly decreases the level of superoxide ions formed by NOS in its absence (3). The binding of BH 4 to iNOS has structural effects in promoting the enzyme dimerization (4 -6), in increasing the binding affinity for the substrate, in shifting the heme spin state from low spin to high spin (7), and in modifying the heme midpoint potential (8). In addition to these structural roles, BH 4 is involved in the catalysis as an electron donor to Fe(II)-O 2 complex (9 -11). Direct evidence for a pterin radical was obtained by rapid freeze-quench EPR (12).According to the x-ray structures of iNOS oxygenase domain, BH 4 makes hydrogen bonds with the heme propionate and extensive interactions with the residues Trp-455, Trp-457, Phe-470, Arg-375, and . Mutation of the residues located near the BH 4 binding site in the oxygenase domain of iNOS shows that hydrogen bonding and stacking modify the extent of dimer formation, the heme environment, and the efficiency of NO synthesis. Specifically, the mutation of Trp-457 into Phe and Ala allowed for dimerization but decreased the NO synthesis activity 3.3-fold and 8-fold, respectively (17). Single-turnover experiments using these mutated proteins followed the formation and decay of Fe(II)-O 2 and the BH 4 radical as intermediates, yielding the ferric complex as the final species (18 -19). These studies showed that Trp-457 ensured a correct rate of electron transfer from BH 4 to Fe(II)-O 2 in the presence of arginine, which maximized the extent of N-hydroxyarginine formed. In the second step of catalysis, Trp-457 modulated the kinetics of N-hydroxyarginine oxidation by iNOS, although the BH 4 radical was n...

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“…The major catalytic mechanism involves one electron processes with 4a-carbinolamine formation from tetrahydrobiopterin (Figure 4). This involves electron donation from tetrahydrobiopterin 1 to ferric iron making 2, the radical cation [49,53]. This is the major mechanism of the enzyme.Oxygen interacts with the radical cationforming an unstable intermediate such as a peroxyl radical or radical hydroperoxide 3.…”

Section: Tyrosine Hydroxylasementioning

confidence: 99%

Parkinson’s Disease—Apoptosis and Dopamine Oxidation

Adams¹

2012

OJApo

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Tyrosine hydroxylase, monoamine oxidase and aldehyde dehydrogenase all form oxygen radicals as part of their mechanisms of action. These oxygen radicals damage dopaminergic neurons in the substantianigra of the midbrain and cause them to die by a process of necrosis or apoptosis. Oxygen radicals quickly abstract hydrogen from DNA forming DNA radicals and causing DNA fragmentation, activation of DNA protective mechanisms, NAD depletion and cell death. Tyrosine hydroxylase is present in all dopaminergic neurons, is involved in the synthesis of dopamine and forms oxygen radicals in a redox mechanism involving its cofactor, tetrahydrobiopterin. Levodopa is used therapeutically in Parkinson's disease patients since it is a precursor for dopamine, an inhibitor of tyrosine hydroxylase, and prolongs patient's lives. Monoamine oxidase converts dopamine into 3,4-dihydroxyphenylacetaldehyde and forms oxygen radicals.Aldehyde dehydrogenase oxidizes the aldehyde and forms oxygen radicals and 3,4-dihydroxyphenylacetic acid. The treatment of Parkinson's disease should involveinhibitors of oxygen radical formation in dopaminergic neurons and neuroprotective agents that stimulate DNA repair and prevent cell death.

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The interconversion of the 5,6,7,8-tetrahydro-, 6,7,8-dihydro-, and radical forms of 6,6,7,7-tetramethyldihydropterin. A model for the biopterin center of aromatic amino acid mixed function oxidases

Abstract: Ausgehend von den Komponenten (I) und (II) werden die Pterin‐Derivate (VI), (VI I) [== Zf‐Oxidationsprodukt von (VI)] bzw. (IX) synthetisiert.

Cited by 61 publications

References 1 publication

The Autoxidation of Tetrahydrobiopterin Revisited

The Autoxidation of Tetrahydrobiopterin Revisited

Dynamic Regulation of the Inducible Nitric-oxide Synthase by NO

Parkinson’s Disease—Apoptosis and Dopamine Oxidation

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