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  Reaction mechanism of GTP cyclohydrolase I: Single turnover experiments using a kinetically competent reaction intermediate

Schramek, N., Bracher, A., Fischer, M., Auerbach, G., Nar, H., Huber, R., et al. (2002). Reaction mechanism of GTP cyclohydrolase I: Single turnover experiments using a kinetically competent reaction intermediate. Journal of Molecular Biology, 316(3), 829-837.

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Genre: Journal Article
Alternative Title : J. Mol. Biol.

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Schramek, N., Author
Bracher, A.1, Author              
Fischer, M., Author
Auerbach, G.2, Author              
Nar, H.2, Author              
Huber, R.3, Author              
Bacher, A., Author
Affiliations:
1Hartl, Franz-Ulrich / Cellular Biochemistry, Max Planck Institute of Biochemistry, Max Planck Society, ou_1565152              
2External Organizations, ou_persistent22              
3Huber, Robert / Structure Research, Max Planck Institute of Biochemistry, Max Planck Society, ou_1565155              

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Free keywords: GTP; GTP cyclohydrolase I; tetrahydrobiopterin biosynthesis; dihydroneopterin triphosphate; pteridine
 Abstract: Elsevier Science Ltd.GTP cyclohydrolase I catalyses the transformation of GTP into dihydroneopterin 3'-triphosphate, which is the first committed precursor of tetrahydrofolate and tetrahydrobiopterin. The kinetically competent reaction intermediate, 2-amino-5-formylamino-6-ribosylamino-4(3H)- pyrimidinone, was used as substrate for single turnover experiments monitored by multiwavelength photometry. The early reaction phase is characterized by the rapid appearance at 320. This species is likely to represent a Schiff base intermediate at the initial stage of the Amadori rearrangement of the carbohydrate side-chain. Deconvolution of the optical spectra suggested four linearly independent processes. A fifth reaction step was attributed to photodecomposition of the enzyme product. Presteady state experiments were also performed with the H179A mutant can catalyse a reversible conversion of GTP to 2-amino-5-formylamino-6-ribosylamino-4(3H)-pyrimidinone but is unable to form the final product, dihydroneopterin triphosphate. Optical spectroscopy failed to detect any intermediate in the reversible reaction sequence catalysed by the mutant protein. The data obtained with the wild-type and mutant protein in conjunction with earlier quenched flow studies show that the enzyme-catalysed opening of the imidazole ring of GTP and the hydrolytic release of formate from the resulting formamide type intermediate are both rapid reactions by comparison with the subsequent rearrangement of the carbohydrate side-chain which precedes the formation of the dihydropyrazine ring of dihydroneopterin triphosphate. (C) 2002 Academic Press.

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Language(s): eng - English
 Dates: 2002-02-22
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: eDoc: 39185
ISI: 000174216400030
 Degree: -

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Title: Journal of Molecular Biology
  Alternative Title : J. Mol. Biol.
Source Genre: Journal
 Creator(s):
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Publ. Info: -
Pages: - Volume / Issue: 316 (3) Sequence Number: - Start / End Page: 829 - 837 Identifier: ISSN: 0022-2836