Biosynthesis of pteridines. NMR studies on the reaction mechanisms of GTP cyclohydrolase I, pyruvoyltetrahydropterin synthase, and sepiapterin reductase.
GTP cyclohydrolase I catalyzes a ring expansion affording dihydroneopterin triphosphate from GTP. [1',2',3',4',5'-13C5, 2'-2H1]GTP was prepared enzymatically from [U-13C6]glucose for use as enzyme substrate. Multinuclear NMR experiments showed that the reaction catalyzed by GTP cyclohydrolase I involves the release of a proton from C-2' of GTP that is exchanged with the bulk solvent. Subsequently, a proton is reintroduced stereospecifically from the bulk solvent. This is in line with an Amadori rearrangement mechanism. The proton introduced from solvent occupies the pro-7R position in the enzyme product. The data also confirm that the reaction catalyzed by pyruvoyltetrahydropterin synthase results in the incorporation of solvent protons into positions C-6 and C-3' of the enzyme product. On the other hand, the reaction catalyzed by sepiapterin reductase does not involve any detectable incorporation of solvent protons into tetrahydrobiopterin.
Institut für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Federal Republic of Germany. Bacher@oc3gra.org.chemie
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Bracher
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Eisenreich
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Schramek
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Ritz
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Götze
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Herrmann
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Gütlich
A
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Bacher
D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D006136:GTP Cyclohydrolase / Q000235:genetics / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D008956:Models, Chemical; D019906:Nuclear Magnetic Resonance, Biomolecular; D019761:Phosphorus-Oxygen Lyases / Q000235:genetics / Q000378:metabolism*; D011621:Pteridines / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012274:Ribulosephosphates / Q000378:metabolism; D013237:Stereoisomerism
D011621:Pteridines; D011994:Recombinant Proteins; D012274:Ribulosephosphates; C031524:ribulose 5-phosphate; D006160:Guanosine Triphosphate; D000429:Alcohol Oxidoreductases; C022630:sepiapterin reductase; D006136:GTP Cyclohydrolase; D019761:Phosphorus-Oxygen Lyases; C043497:6-pyruvoyltetrahydropterin synthase