title: Temperature-dependent presteady state kinetics of lumazine synthase from the hyperthermophilic eubacterium Aquifex aeolicus.
abstract: 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.
authors.affiliation: Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany.
authors.forename: Ilka
authors.initials: I
authors.lastname: Haase
authors.forename: Markus
authors.initials: M
authors.lastname: Fischer
authors.forename: Adelbert
authors.initials: A
authors.lastname: Bacher
authors.forename: Nicholas
authors.initials: N
authors.lastname: Schramek
mesh_terms: D005051:Eubacterium / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism*; D012256:Riboflavin / Q000096:biosynthesis; D013696:Temperature; D013816:Thermodynamics
chemical_list: D009097:Multienzyme Complexes; C044822:6,7-dimethyl-8-ribityllumazine synthase; D012256:Riboflavin