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          Institute: MPI für Biochemie     Collection: Structure Research (R. Huber)     Display Documents



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ID: 39185.0, MPI für Biochemie / Structure Research (R. Huber)
Reaction mechanism of GTP cyclohydrolase I: Single turnover experiments using a kinetically competent reaction intermediate
Authors:Schramek, N.; Bracher, A.; Fischer, M.; Auerbach, G.; Nar, H.; Huber, R.; Bacher, A.
Language:English
Date of Publication (YYYY-MM-DD):2002-02-22
Title of Journal:Journal of Molecular Biology
Journal Abbrev.:J. Mol. Biol.
Volume:316
Issue / Number:3
Start Page:829
End Page:837
Review Status:Peer-review
Audience:Not Specified
Abstract / Description: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.
Free Keywords:GTP; GTP cyclohydrolase I; tetrahydrobiopterin biosynthesis; dihydroneopterin triphosphate; pteridine
Comment of the Author/Creator:Date: 2002, FEB 22
External Publication Status:published
Document Type:Article
Communicated by:N.N.
Affiliations:MPI für Biochemie/Structure Research (Huber)
MPI für Biochemie/Cellular Biochemistry (F.-U. Hartl)/Research Group A. Bracher
External Affiliations:Tech Univ Munich, Lehrstuhl Organ Chem & Biochem,; Lichtenbergstr 4, D-85747 Garching, Germany; Tech Univ Munich, Lehrstuhl Organ Chem & Biochem, D-85747 Garching, Germany; European Mol Biol Lab, F-38042 Grenoble 9, France; Antisense Pharma GMBH, D-93053 Regensburg, Germany; Boehringer Ingelheim Pharma, D-88400 Biberach, Germany
Identifiers:ISI:000174216400030 [ID No:1]
ISSN:0022-2836 [ID No:2]
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