The biosynthesis of one riboflavin molecule requires one molecule of GTP and two molecules of ribulose 5-phosphate as substrates. GTP is hydrolytically opened, converted into 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione by a sequence of deamination, side chain reduction and dephosphorylation. Condensation with 3,4-dihydroxy-2-butanone 4-phosphate obtained from ribulose 5-phosphate leads to 6,7-dimethyl-8-ribityllumazine. The dismutation of 6,7-dimethyl-8-ribityllumazine catalysed by riboflavin synthase produces riboflavin and 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione. A pentacyclic adduct of two 6,7-dimethyl-8-ribityllumazines has been identified earlier as a catalytically competent reaction intermediate of the Escherichia coli enzyme. Acid quenching of reaction mixtures of riboflavin synthase of Methanococcus jannaschii, devoid of similarity to riboflavin synthases of eubacteria and eukaryotes, afforded a compound whose optical absorption and NMR spectra resemble that of the pentacyclic E. coli riboflavin synthase intermediate, whereas the CD spectra of the two compounds have similar envelopes but opposite signs. Each of the compounds could serve as a catalytically competent intermediate for the enzyme by which it was produced, but not vice versa. All available data indicate that the respective pentacyclic intermediates of the M. jannaschii and E. coli enzymes are diastereomers. Whereas the riboflavin synthase of M. jannaschii is devoid of similarity with those of eubacteria and eukaryotes, it has significant sequence similarity with 6,7-dimethyl-8-ribityllumazine synthases catalysing the penultimate step of riboflavin biosynthesis. 6,7-Dimethyl-8-ribityllumazine synthase and the archaeal riboflavin synthase appear to have diverged early in the evolution of Archaea from a common ancestor.
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Conference Article|
August 01 2005
Structures and reaction mechanisms of riboflavin synthases of eubacterial and archaeal origin
M. Fischer;
M. Fischer
1
1Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany
1To whom correspondence should be addressed (email markus.fischer@ch.tum.de).
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W. Römisch;
W. Römisch
1Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany
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B. Illarionov;
B. Illarionov
1Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany
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W. Eisenreich;
W. Eisenreich
1Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany
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A. Bacher
A. Bacher
1Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany
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Publisher: Portland Press Ltd
Received:
April 12 2005
Online ISSN: 1470-8752
Print ISSN: 0300-5127
© 2005 The Biochemical Society
2005
Biochem Soc Trans (2005) 33 (4): 780–784.
Article history
Received:
April 12 2005
Citation
M. Fischer, W. Römisch, B. Illarionov, W. Eisenreich, A. Bacher; Structures and reaction mechanisms of riboflavin synthases of eubacterial and archaeal origin. Biochem Soc Trans 1 August 2005; 33 (4): 780–784. doi: https://doi.org/10.1042/BST0330780
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