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.
Bracher
A
A
Institut für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Federal Republic of Germany. Bacher@oc3gra.org.chemie
Eisenreich
W
W
Schramek
N
N
Ritz
H
H
Götze
E
E
Herrmann
A
A
Gütlich
M
M
Bacher
A
A
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