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J Biol Chem. 2003 Sep 26;278(39):37909-15. Epub 2003 Jul 16.

Temperature-dependent presteady state kinetics of lumazine synthase from the hyperthermophilic eubacterium Aquifex aeolicus.

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  • 1Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany.


6,7-dimethyl-8-ribityllumazine synthase (lumazine synthase) catalyzes the condensation of 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione and 3,4-dihydroxy-2-butanone 4-phosphate. Presteady state kinetic experiments using the enzyme from the hyperthermophilic bacterium Aquifex aeolicus were monitored by multiwavelength photometry. An early optical transient absorbing around 330 nm is interpreted as a Schiff base intermediate obtained by reaction of the position 5 amino group of the heterocyclic substrate with the carbonyl group of 3,4-dihydroxy-2-butanone 4-phosphate. A second transient with an absorption maximum at 445 nm represents an intermediate resulting from the elimination of orthophosphate from the Schiff base. The rate-determining step is the subsequent formation of the 7-exomethylene type anion of 6,7-dimethyl-8-ribityllumazine. The rate constants for the three partial reactions identified by the stopped flow experiments show linear Arrhenius relations in the temperature range of 15-70 degrees C.

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